Unbodied "Psionic Trickster"

Gimmick: An unbodied that does decent damage with her natural touch attack (sneak attack) while retaining her psi abilities.

Drawbacks: No such thing as a Psionic Trickster, couldn't have 10 levels in said class if it did exist.

Alternate options: Straight rogue or ninja. Wis to AC would be quite nice as unbodied are hurting for AC sources (yet hard to damage anyways) one level of telepath to get level 3 powers (+1feat)

Payoff: I imagine playing an incorporeal creature could be lots of fun. Level 10+

Pixie

Gimmick: DR 10/cold iron, high SR, improved invisibility, flight and great stat bonuses appears to be pretty overpowered to me (except for a melee fighter concept). Ideally, an arcane trickster with feats to maximize her sneak attack damage.

Redeemed Wight (LM monster class) adventurer

Gimmick: Undead advantages, good stealth and an interesting concept for a 'retributive' figure who hates herself enough to battle the forces of evil that led to her creation.

Options: Rogue, Ninja, undead hunting monk/ranger

Half-Dragon Orc or Half-Dragon Centaur

Strong guy krush. +12 STR for +3 EL and +16 for +9 EL, respectively. Half-Dragon Ogre is another option (+18 STR), but for the same EL as a Centaur, they don't seem quite as potent.

Four energy immunities?

Be a lich with an immunity-granting bloodline. Then take a prestige class that grants immunity (elemental savant gets you some caster levels) and you could have 4 .

3 bloodlines, 3 wizard, 9 savant, gets you the 6th level spells you need to take 4 lich. Efreeti blood, earth savant, perhaps. Then you take that last level of savant--since only humanoids can become Liches :)

Focused Specialist Master Specialist (evoker)

The ultimate blaster. Pick a prestige class (Master Specialist finishes aftert 13) that increases save DCs/caster level--archmage, for example, wouldn't be too bad since you've got the spell slots to spare.

Brass Dragon, using this monster class i'm working on.

Drawbacks: playing a dragon means little variety

Payoff: I'm playing a freakin' dragon!

Toughest Dwarf

dwarven monk/defender

alt monk
Gain
Damage reduction (as barbarian).
Lose
Enhancement bonus to unarmored speed, bonus to Armor Class when unarmored (retain Wisdom bonus to AC when unarmored).
Undying Way
Monks of the Undying Way believe in patience above all else. They work to outlast their opponents by means of superior endurance.

1st-Level Skill Bonus: Concentration.
1st-Level Feat: Toughness.
2nd-Level Feat: Endurance.
6th-Level Feat: Diehard.
6th-Level Bonus Ability: When fighting defensively, using Combat Expertise, or using the total defense action, the monk gains damage reduction 2/-.
Prerequisites: Concentration 9 ranks.

nice thing about this is prereqs for defender include toughness and endurance (and dodge), and base attack 7. So at level 20 you've got DR 8/-, 10/- when using expertise or fighting defensively, and hell, you could have taken resilience to have 9/ and 11/. might as well ditch wisdom to AC to get adm. full plate and Armor Focus for another 5/-, but then you lose improved evasion (armor focus is only med. and hvy armor)
also, with half-dragon template instead of 3 levels monk, you could take the endure blows feat (dr 2/-) provided you have con 19. as a half dragon dwarf that wouldn't be too hard. but it only gets you 1 more DR (since you lose 1 point of your monk DR) as well as 3 levels of saves, miss out on +16 BAB, improved evasion.. probably not worth it. but the +8 strength...

1 (monk 7) + 2 (undying way) + 2 (endure blows) + 6 (defender) + 1 (resilience) + 3 (adm. full plate) + 2 (armor focus) = 17

-a half dragon breath specialist, uses metabreath feats (because who cares if you can't breath again for 10 rounds when you can breath only once per day?) - then again the dragon breath feat is specifically for half-dragons and allows them to breath however often (only once every 1d4 rounds)

(combine the two?)

Constructor - Because astral construct 9 with 4 menu C abilities is just sick, sick, sick. 

(Elan?) Psion (shaper)

Feats: Boost Construct (1st)

Possibly: Eptopic Form x2 (Emerald Gyre (i.e. improved grab), then Scorpion boy). Overchannel could be good to make bigger constructs. Practiced Manifester erases the loss of 2 caster levels. Some metapsionic feats might be ok, but expending focus negates some of the constructor's ability (especially 1min/level constructs), see below.

So, the basic plan is psion 5 constructor 10 ?? 5

 Constructor is a totally excellent, BS class that can be found with a couple other gamebreakers here, at the Wizards site. 

At level 10, suggested abilities for your construct (5) might be: (A) Improved Slam Attack (A) Trip (B) Extra Attack (B) Pounce, for a tough charger, or perhaps (A) Celerity (A) Armor Spikes (B) Trample (B) Muscle for a DC 24 reflex save or take d8+d6+11 damage.

Some Dragon Slayer -very feat heavy, but wow. so you take dragonfoe and dragon doom, use a keen scythe (or improved critical). have a psionic focus/wild talent, and the one that lets you auto-confirm a crit. then, as many luck feats as you can get (complete scoundrel probably has a class that gets them). you attack the dragon w/your dragonbane scythe, use true strike, max your power attack, reroll as many times as you can w/your luck feats (luck domain granted power, too), hoping to get the 10% chance to crit... then if you do, automatically confirm it (of course if using a reroll is a swift action it's only kind of cool) and do like, a bajillion damage to it. would work with favored power attack too, 1 ranger and scout is nice to get favored enemy and make sure you don't suck all the time.