Cakewalk or Waves 1176s on all sorts of things. Not much to choose between Cake and Waves with those two other than the Cakewalk one is Sonar only. They do sound a little different, Waves' plugin has two different models of the 1176 and the 'black' version is pretty much the same as Sonar's 1176 while the "blue" models an older version of the comp and does sound and react noticably differently. I probably use 1176 style compressors mostly.
Cakewalk's CA-2A, especially on bass guitar/synth. The attack and release character 'just works' on low pitched instruments somehow.
Bozdigital +10dB, works on most things pretty well, but I find it particularly good for guitars and strings generally that need a bit of subtle assistance. Also does a very good job on drums.
The compressors in Waves TG12345 channel strip emulations get used when I feel like pretending I'm in a very well equipped world-class studio in 1977.
Waves One Knob Pumper is a sort of compressor I find useful for well, pumping stuff.
I've also got a couple of old Alesis 3630s in a rack that get used once in a rare while. Hi-fi they're not, but their cheap and nasty thing comes in handy sometimes. Actually, they're not quite as bad as some would have you believe once you understand their limitations.
For limiters I seem to keep going back to Cake's Concrete Limiter and Waves' L2. For multiband compression Waves C6 usually.