Bind Vestige/Improved Bind Vestige/Practiced Binder seemed like very compelling feats for epic E6 characters, especially noncasters, when I looked at them. They provide so much flexibility and binder powers are generally oriented towards mixing it up, or else subbing for another class in a pinch. A fighter, barbarian, rogue, monk, etc. gets a lot for the xp by choosing these.
On the other hand, I hadn't looked at the SLA feats in Complete Arcane, because I'd banned them for flavor reasons, but if you piled up, say, Communicator, Insightful, Night Haunt, and Spell Hand, all of a sudden Grog the Barbarian has a little sideline as a utility caster, or Frazzt the wizard just opened up a lot of spell slots.
It's a little outside the scope of the thread, but I had considered adding a capstone feat for 6th-level binders that lets them bind two vestiges at once, since the class seems a little weak otherwise.
The one big feat book that's missing here is the Player's Handbook II.