Waves has got the best software compressors I've ever found - They do sound much better than the regular plug-ins, I use Waves C1 and Renaissance compressor all the time... Their Renaissance EQ is useful too, sounds more musical than most digital EQ.

You'll really notice how good the compression is when you're doing transient boosting - Like using a 30ms attack, 4:1 ratio, 6db's gain reduction, fast release on a bass drum - To get that real punchy style of compression - It doesn't work atall with most plug-ins, but works fine with Waves - I'd even say ALMOST approaching a decent hardware compressor in some ways - Maybe not quite as fat sounding, still a little clinical.

Oh yeah, Waves Ultramizer is alright too for pumping mixes up, and the Stereo Imager is really useful - It's pretty much the only software effects I use these days, mainly for compression.