The Raptor's Mask from MiC (p. 210) has a pretty unique effect.
Namely, it renders you immune to any effect that would blind or dazzle you.
Note that I didn't say that it rendered you immune to blindness or being dazzled. No, it renders you immune to any effects that include dazzling or blinding you.
This means that a creature with fewer than 8 HD would be entirely immune to effects of a Prismatic Wall (by RAW, at least).
And it's only 3500 gp, which is a pretty reasonable price even if you go by RAI.
On a similar note, a Shirt of Wraith Stalking allows you to use Hide from Undead at-will, and intelligent Undead don't get a save. And it's only 6000 gp.
Edit: Amulets of Teamwork aren't that bad, either - 2000 gp to boost your Aid Another bonuses from +2 to +3, and anyone flanking a creature you're flanking gets a +2 untyped bonus to damage. If you let the bonuses from different Amulets stack (it is an untyped bonus, after all), you can get some pretty nice damage bonuses. And add a 1/day +5 Competence bonus to AC for you and an ally that lasts a round, and you've got a pretty nice item, all things considered.
Bracers of the Blast Barrier are nice for Warlocks; 3200 GP for the ability to make short-lived walls out of your Eldritch Blast 3/day.