These Waves plugins are considered "standard" for all professional recording studios.

Axx: Its almost as good as actually re-amping a track.
Bass: If used sparingly, this can "fatten" up a track and still retain articulation and dB level.
Channel: If my computer could handle it, I'd have one of these on every channel.
De-Ess: Suppresses severe siblance satisfactorily
EQ: Best sounding EQ plugin on the market.
Reverb: Generally considered a kick-ass reverb.
Vox: Simple, effective, I use it a LOT.