Soundplant - Play sound files with the computer keyboard
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
CasterSoundboard - A soundboard for hot-keying and playing back sounds. (For podcasting)
Kontakt - With KONTAKT 6, you can sound like a snare drum, a symphony orchestra, or anything in between, from a universe of sampled instruments.
JN Soundboard - An open-source hotkey soundboard program
GSnap - With GSnap you can get an auto-tune effect.