Agile Opportunist (PHB2)
The rating assumes you don't have a Cunning Bard in your party. If you do, it's an extra attack once a around when you're missed, and that's kinda useful .
Arbiter of Justice (D382)
The key here is going to be the "pretend you dropped someone your ally drops/bloodies". In the cookie-cutter case, this means the feat reads "Buy a Reaper's Gauntlet Axe, for the free MBA+Shift even if an ally does the deed". Clear the cheese factor with your DM first. Oh yeah, +2 damage about half the time. May not even be worth remembering.
Armored by Faith (DP)
Temp hitpoints, 1/encounter. Better if you've taken a PP or ED that allows you multiple channel divinities per encounter.
Avenging Surge (DP)
The problem is that Unitarians take out monsters in parties. If you're in the middle of the scrum, the monster will be attacking your defender, not you... at which point why are you giving yourself temporary hit points? But boy are temp hp tasty, especially if you have to double as a defender every once in a while. Defengers love this feat.
Blood Thirst (PHB)
Thematic. If you have lots of attacks, it can matter, but you'll like be 40th level before a +2 static feat fits in.
Censure's Grip (DP)
For the off-tank, a great feat. You can easily, permamently, keep monsters from shifting away (and your OA will usually keep them from moving away). There's also a nice epic combo with radiant zones you can stick them in. For chasers, another trap . Monsters don't run already, why make it harder on them just in case they might.
Clinging Radiance (DP)
Stops lurkers cold... Is that an issue frequently enough to be worth a feat? And isn't your perception already sky high?
Danger Sense (PHB)
The Martyrs among you like going first to quickly get surrounded and rack up silly high bonuses. But, humorously enough, your Dex isn't that high. This helps fix the problem. Stack with Improved Initiative, and you'll go first more often than not.
Defensive Advantage (PHB)
+2 to AC when you have CA. As an Avenger, you can frequently have CA, but it's harder to guarantee than, for example, a rogue. (You'll usually get it via Deadly Draw , which requires that you hit the target with a pull or slide power). Add in the way that AC can already be plenty high, and I don't see it being worth a feat in the vast majority of situations.
Devastating Critical (PHB)
Another feat for the Crit Fisherman... Except it just doesn't add enough to DPR to justify the feat slot.
Devout Guidance (DP)
Divine Guidance is a really good Channel Divinity power, and this makes it better. Worse in a better party , where just granting the reroll is good 'nuf.
Eager for Blood (DP)
Only interesting if combat only lasts one round, which will not be a stable situation (the DM will adjust). Once that's no longer the case, Weapon Focus or the like will be better, and that's still assuming fairly short combats.
Exposing Oath (D382)
This is for radiant focused Avengers, who end up fighting outsiders far too often. For everyone else, pass. Very few monsters you'll face are resistant to radiant.
Fleet Footed (PHB)
I like speed. Speed is good. However you're likely going to have +speed boots. Make sure you have enough speed, not too much speed.
Halo of Isolation (D382)
This should help you keep your oath, at least if you stay close enough to your fighter. This won't let you pretend to be a defender, because anyone can still shift away... which you'll normally consider a feature.
Inexorable Pursuit (PHB2)
Charging through enemies is the real draw. But if that's what you want, look for the Phasing powers. Inexorable Pursuit is also a level 7 power that lets you charge through enemies once an encounter, and that's likely enough. Ghostly Vengeance (daily u22) gives it to you for the entire encounter.
Invigorating Critical (DP)
Humorously, this is worse for those that actually have good crit ranges : Because you'll crit too soon in the battle, and not be able to use the healing.
Onslaught of Enmity (PHB2)
The main use case here is: Your target died last turn, so now you need to melt a new target. And you've still got a minor action attack. Here's your approach power.
Unfortunately, at rational levels you'll only have one minor action attack. At higher levels, Soul Forge Hammering can be relevant here.
Painful Oath (D382)
Free DPR, and a good amount of it. It doesn't work with multi-attacks, but you don't have a lot of multi-attacks, so this is pure tofo whacking DPR. Take it. Really.
Note, "Once per turn" means that you get it on opportunity attacks as well.
Paragon Defenses (PHB2)
Obsoleted by Improved Defences from HotFL
Pervasive Light (DP)
If you have Punishing Radiance (Epic) or an ally who's the party's Morninglord , this is lots better . If you are a Morninglord , you do radiant damage, so the feat's irrelevant. If an ally is, this feat frees up your weapon choises, and lets you still ping the radiant Vuln on your off-action attacks. But even if you don't know any morninglords, there's a nice combination with Power of the Sun (DP).
Protected Isolation (PHB2)
Another bad feat to keep those enemies that are screwing up your oath from giving you Retribution bonuses. Technically is not a trap, but will work as one against most DMs.
Pledge of Retribution (DP)
If you miss enough for this to matter, you're doing something wrong.
Psychic Lock (PHB)
You have a decent number of psychic powers, but they are split evenly between Implement and Weapon powers, and are not usually the first choice. The feat won't make them the first choice powers either.
Reserve Maneuver (PHB2)
Are you taking some weird PP to get high-crit, and don't know what to do with your PP encounter power? Well, why don't you replace it with Fury's Advance or some other class power? (If this includes your multiclass, it's even better.)
Scimitar Dance (PHB)
Easy enough to qualify. But you don't have a two-weapon at-will power, and you don't miss much. Ranger going Half-Elves might consider it, but should then remember that their Dexterity isn't all that anyway.
Secret Stride (PHB)
Lets the Ninja stay invisible longer.
Uncanny Dodge (PHB)
For those who frequently get surrounded, this might help you control the rate of taking hits.
Two Weapon Opening (PHB2)
This is a great DPR feat, except that it requires you to use smaller weapons, and doesn't stack with other free-attacks on crits.