Well for the money, you can`t beat the sonalksis stereo compressor.
It is one of the very very few vsti compressors that truly handles like hardware.
The way it handles transients and the way the attack works is just amazing.
Can`t emphasise enough how amazing this compressor is.
DSP cards are great too. I`ve got the Liquid Mix, which is simply amazing.
URS compressors are really nice.

Voxengo Marquis is a really stunning compressor, and again has a very good hardware like response.