One I've come across that is up to pro standards is the Waves Compressor, but it's not free. Personally, I like that one so much that I use it on everything. The only thing I always use analogue compressors on is bass guitar lines, then I reshape them again with the waves compressor.
http://www.waves.com...ent.aspx?id=171
I would defy anyone to tell the difference between that and an analogue unit in a mix
Alternatively, you can pick up a Behringer Composer Pro for less than a hundred dollars. Every studio should have a Behringer Composer in it. I've just bought a dbx compressor this weekend, but haven't had a chance to try it out yet.
Despite what I'm about to say next, I think we're all getting far too technology oriented in mixing. I think the performance aspect of mixing has been lost in the modern era and the mixes of today are far too flat. I think it's better psychoacoustically if they have edges to them. In order to make my mixes stand alongside aforementioned modern products, I would recompress the audio sample loops to reshape the peaks. Not too much, maybe just shaving two or three decibels. A mix sounds a lot tighter if the compressor release settings on all the individual tracks are a related to each other as a function of rational numbers. Most sound engineers, even pro ones, have a tendency just to twiddle the attack and release times until they think it sounds pretty. Personally, I always walk the extra mile and do the maths.
60,000 / BPM = time of each quarter beat in milliseconds. By dividing or multiplying this number by two until it falls into the parameters you want, you can have a tight, tempo based mix.