+1 to waves SSL channel strip, I use it often. And I love the bus compressor.
Great for guitar and drum bus, and I've enjoyed doing a bit of "in the box" mastering with it, as well.
UAD's Neve-based channel strip is pretty sweet.
I don't have experience with Sonalksis or API (I'm poor...),
but I'm sure they sound great. I'm a sucker for channel strips.
Its just so convenient having everything you need right there.
Wow, there are so many great plugins. I use the Focusrite Liquid Mix (hardware plugin) on every mix, mostly for compression but the eq gets some use as well. As for gating, I always do it as a process (I use Adobe Audition) in the wave editor and save the new track under a different name, that gives me the chance to review it and make sure I caught all the naunces (especially on snare) and to get rid of any false triggers. Audition also has many built-in plugs that are very nice.
No one wants to admit they "like" plug in's, I'm afraid.
I like Digi's SMACK! a lot. Also like nearly all the massey plug in's. Their de-esser is to die for. Re-vibe is a fave on the reverb. Also like TL Space (if you have HD). Oops, I think Re-Vibe may be HD only too. Not sure. Love the EMI Compressors too. They're touchy and have the ability to be drastic and are really cool.