So many enchantes, so little time. Are they any good? Here's what I think. Have a drastically different opinion on any of these? Send me an email with your bard's name and your two cents worth and I'll post it, hopefully painting a fair and balanced picture of the song in question. Also, if I'm flat-out wrong with any of these  statements, let me know!
Many thanks to Mickalai for providing some quality control.

Five Star Enchantes

• Hodierna's Lilt Restores health, fatigue, and concentration for all player characters who hear it, along with boosting the First Aid skill. This song will save your life so many times when your vitality is in peril. If you're nice, you can save someone else's life, too! Empaths will love you for performing this song while they're taking wounds from folks.
• Demrris' Resolve Instills fear in those not in your group, giving them the gift of roundtime plus forcing them into a compromising position depending on your ability, from a mere flinch up to complete immobilization!  This song will allow you to kill something that is normally out of range for the weapon you're using. This song will also save your life if you're swarmed and cannot retreat. Follow it up with a Piercing Whistle for a potent escape bid.
• Desert's Maelstrom Kicks up a bunch of wind and dust, causing several effects: your group's balance is boosted, your enemies' balance is nerfed, ranged weapons get nerfed, your overall defensive skill appears to get boosted, and it cleans up junk that's lying around on the floor! Just as Resolve allows you to overhunt offensively, Maelstrom allows you to overhunt defensively. And we all know overhunting=faster learning. You're nuts!

Four Star Enchantes

• Naga's Blessing Drastically increases the speed at which magic users in the area recover their attunement to the mana streams (i.e.  their mana bar refills faster). Remember, empaths use a lot of mana when healing themselves, and clerics use a lot when they're resurrecting farm buyers, so both of them will love you when you perform this song in a triage room.
• Drums of the Snake Provides a strong boost to the Climbing, Skinning, Disarm Traps, and Lockpicking skills, as well as Agility. It will also reduce the roundtimes for disarming and lockpicking boxes. Even better, the effects of the song will linger around for a bit after you stop playing it (length depending on how long you played it for), so it's possible to start it up and stow away your instrument before making that tough climb or popping that troublesome box.
• Merelew's Legacy bonuses your Swimming skill, allows you to breathe underwater, and can snuff out a warrior mage's Mantle of Flame, along with nerfing other fire magic as well. This enchante has an amazing record for teaching the vocals skill exceptionally well. Plus, it repeats at the end, making it the only song that never ends...
• Rage of the Clans Gives a boost to the power and accuracy of all attacks for all player characters in the room. The effect of this song is quite potent, and it makes a fine compliment to Demrris' Resolve if you have a bardic hunting buddy.
• Glythide's Joy Protects your group from targeted magic (like lightning bolts, etc.), either by weakening them, or by completely nullifying their effectiveness. This is particularly effective against critters that can one-hit kill you with magic. 
• Harmony- Gives a buff to virtually every combat skill you have, along with helping to maintain your balance. When sung Loud, it places a heavier empahasis on the song's offensive buffs, and when sung Quiet, it does likewise for its defensive buffs. This song is extremely hard to put mana into, relatively.
• Damaris' Lullaby- Can potentially put everything that opposes your group to sleep within two pulses of the song, leaving them incredibly vulnerable to attack. This is a devastating enchante when you are in a group facing many, many foes (such as during an invasion or mass hunting trip). There are two drawbacks- one, it is only played on stringed instruments, thus leaving you with few offensive combat options, and two, once you have stopped playing the song, it can not be played again for several minutes.

Three Star Enchantes

• Faenella's Grace Provides a Scholarship boost to all that hear it, making listening to and teaching classes much more effective. This song will also help you read a scroll that would normally be too hard, and to more successfully Recall History in appropriate spots, among other perks. A must for bards who like to bum around the major hangout spots a lot.
• Misdirection Gives those in your group a boost to Hiding and Stalking, and also penalizes the Perception of those outside your group. While you will be pulled out of hiding whenever this song pulses,  this drawback can be worked off with enough Hiding skill (approximately 200 ranks). An absolute must for stealth-bards who wish to take the sting out of training Hiding.
• Nexus Boosts the elemental mana in the room, plus gives an apparent boost to Primary Magic to all magic users in the room. When combined with the warrior mage spell Etheral Fissure, dizzying amounts of mana can be created. This is a good song to perform in a triage setting when Hodierna's Lilt and Naga's Blessing are already being peformed by other bards.
• Resonance Forms a bond between you and the melee weapon in your right hand, provided you have enough skill in that weapon. Your offensive ability with that weapon and your Parry skill both get a healthy boost. Outputting some of the weirdest messaging in the game, Resonance can be quite troublesome if you tend to sheathe your weapon a lot during combat, as the song can cause your weapon to leap back into your hand.
• Abandoned Heart Drains the fatigue of those not in your group, plus turns any bleeders they may have into gushing fountains of red goodness. It has been hinted that a third effect can be attained with enough mana. This song is an excellent followup/compliment to Phoenix's Pyre and nice bottle of naphtha.
• Caress of the Sun This song will dry those in your group, along with any wet instruments or spellbooks you happen to have in your possession. This song also prevents said implements from becoming wet, even if you're standing out in a rainstorm with them. Very handy. Caress of the Sun also provides you with a resistance to cold attacks, such as a warrior mage's Frostbite. It's also worth mentioning that this enchante is the best way to learn the Vocals skill before you're able to get Merelew's Legacy.
• Chorus of Madmen Seriously messes up everyone it affects with very random effects, including self-harm, difficulty concentrating and using magic, stuns, and very occasionally, death. It frequently causes many short bouts of roundtime to its victims, too.
• Redeemer's Pride Boosts resistance to fear-based effects for those in your group. Given that very few critters in the game currently use these types of attacks, this facet of the song is lacking. It is worthy to note that this enchante will somewhat protect against the effects of barbarian roars or another bard's Demrris' Resolve. This enchante now also boosts the Multi Opponent skill of your group, and is a very excellent song to use when you can confidently hunt a creature without magic, and wish to take on three, four, or more of them to continue training your defenses.

Two Star Enchantes

• Eillie's Cry Enchants your body so that if you die, all bards in the vicinity see a vision of the room you're in. This is also the only song you can perform post-mortem! Other bards can then sing the song themselves to signal to you that they heard you and that they're coming to the rescue (hopefully). Very good for young bards who hang around crowded areas like the Crossing or Riverhaven.
• Eye of Kertigen Provides a boost to your Perception, then with more mana will create a soft green glow around your body, allowing you to see in the dark, then at even higher mana levels will periodically sweep the room and pull other players out of hiding. A strong utility enchante to use while juggling or merely being vigilant.
• Naming of Tears Provides your group with a boost to their Evasion skill (the best of any enchante), as well as creating a sonic shield that can absorb damage to lessen the strength of blows to you, with to potential to save you from what would otherwise be a one-hit-kill. This enchante is relatively weak until the upper mana-levels are reached.
• Albreda's Balm Calms those not in your group into a state of passiveness, preventing them from attacking anything, much like the paladins' Banner of Truce. Not a bad song to perform if you or someone you know is trying to dig out a grave or engage in some other non-combat activity in a combat zone.  Also, for young bards who cannot yet get Demrris' Resolve or Piercing Whistle, this song fills the "panic button" slot fairly well.
• Aura of Tongues Allows you to understand languages you normally could not. The more mana you put in, the more you languages become clear to you. A niche enchante, it is the only ability in the game that allows such an effect. To avoid telltale messaging to others in the room, perform it on a stringed instrument instead of singing it.

One Star Enchantes

• Phoenix's Pyre Heats up the air around you, beefing up the power of any fire-based spells being used in the room, plus igniting naphtha that anybody happens to be, uh, wearing. A must for those who train Light Thrown, as throwing a bottle of naphtha at a target while performing this song has incredibly devastating effects, especially when followed-up/complimented by Abandoned Heart. Pyre also deals extremely modest damage to your enemies, being more effective the closer they are engaged to you. 
• Aether Wolves Scares the pants off of those not in your group, causing them to hastily retreat from you, or even book it into the next room! Sworn ally to several ranged-weapon-using bards, this song seems to pulse a bit too infrequently to be effective. It can be fun, though, to send a horde of ten critters running into the  occupied room next to you.
• Sanctuary With enough mana, this song will prevent you from being pinpointed by means such as a moon mage's Locate spell or a warrior mage's familiar. It also might make critters slightly less likely to come wandering into the room, though this might just be coincidental. Not a very useful spell.

Pertinent Links

• Dewsong's Enchante Tree- A good linear visualization of all current and planned enchantes.
• Shavay's Enchante Chart- A colorful variation; also contains information for each enchante, like key and tempo.