Well, I was specifically looking at making a rogue build that utilized the Riposte strike often.
With that at-will, use
Vigilante Justice Style from Art of the Kill, Dragon 373. The attacked creature doesn't have to attack you to create the interrupt attack, just someone adjacent to you. So, you flank a guy and then attack with it, and as a move action, shift so that you are now adjacent to your flanker.
With Cruel Cut and Impending Doom style from the same, if you hit with the interrupt attack the target takes Wisdom mod ongoing damage (save ends) and -2 to attacks until the end of your next turn.
With Grudge Style and Warborn Fury style of arena feats from We who are about to die, dragon 368, you get with a successful attack with the interrupt attack a -3 to hit to the triggering attack, and -2 to AC and Reflex of the target's defense until the end of your turn.
So you use this, shift, and if the target attacks you or your buddy you attack him with the interrupt. IF the interrupt attack hits, the triggering attack of the enemy is at -5 to hit, the rest of his attacks until the end of your next turn are at -2, he's at -2 to AC and Reflex until the end of your turn, takes ongoing damage equal to your Wisdom (save ends).
So, yeah, in all fairness it is 5 feats to really beef the heck outta one at-will, but it does make that at will pretty nice. I don't think broken considering the amount of feats invested. But I like it nonetheless, and was wondering what others thought.