Shambling Mound's electricity immunity is nice; it's hard to go wrong with a near-infinite Con score.
Runehound's have 500' blindsight.
I sense plenty of untapped potential in the Epic Level Handbook's creature section.
I know this doesn't help with tasty Ex abilities, but it seems like a few choice castings of Ability Rip from Serpent Kingdoms would be a much simpler way of going about this.