I'll second the presonus MP20... cool, weird, useable on a lot of things...
API 512c modules (c'mon at $500 a pop they ARE cheap)
Zoom RFX-2000 (I call it the "Destroyer of Sounds" good if you need to mess up things pretty badly)
Boss RPS-10 (Just feed something through and watch it mess up everything as a pitch shifter... it's... unique
)
Safe Sound Audio P1 (Very cool preamp, borderline genius design... seriously)
DAV BG-1 (Great little pre, I prefer the rackmountable BG-2 but it's three times the price)
Ashly SC-50