Several plugin companies have emulations of the SSL 4000 series bus compressor. Cakewalk, NI and Cytomic come to mind, but I'm sure there are many more.
 
I did try the demo of Cytomic's "The Glue" a while back and found the presets really useful (uncommon for a compressor plugin IMO). But it's $99 and I'm unsure whether it's worth it if the ProChannel S-type bus comp (which I've been using to good effect) has the same basic capability.
 
How about the other offerings? Which do you prefer and why? Do some models "sound" better than others? Comparisons to the PC module are appreaciated!
 
Sven

The Waves SSL 4000 Bus compressor is amazing...

It's got to be the best SSL 4000 Emu out there and, as far as SSL Emu's go, it's the "Elmers" of mixing ITB IMHO...

But it's pricey...$650 Retail for the SSL 4000 Collection

I have the Glue and love it on the 2 bus. I just got the beta version of the free TDR Feedback Compressor and, in limited testing, I think it might be as good (though not modeled after any hardware comp). Couldn't hurt to give it a try.

This review compares a bunch

http://www.soundonsound.c.../articles/the-glue.htm

I used to have The Glue, but sold it after buying the Waves SSL bundle because I didn't need the redundancy.  During the short period that I had both, I compared The Glue to the SSL buss comp a few times and didn't really hear enough difference to warrant keeping both, although The Glue obviously has far more options and is more flexible.  I don't recall comparing it to the Pro Channel S-type, unfortunately.  Also, I've never used a real SSL buss compressor, so I can't tell you if one was better than the other at emulating the real thing.

Thanks for the replies. The SoS review was very helpful! I think I'm pretty much set (pun intended) on The Glue. The extra controls seem real useful, even if it might not be the most accurate SSL emulation. 

It's also less expensive than Waves or UAD.

I have had The Glue for some time and it is now all I use - it is very good and very easy to use - I have tried some of the other options but simply cannot see nor hear that they are any better (or any worse) than the The Glue, if you see what I mean!!!
Cheers
Nigel

The Glue is also my main comp for the drum bus. Gives a nice 'pop' and you can parallel compress with the mix knob.

I'm waiting for the release of Slate Digital's VBC.  Analog emulations of four compressors. Can't wait to try these.