Channel eq. Followed by spectrum/correlation analysers such as Span and a few other "utility" plugins.
I could, at a push, do pretty much everything in hardware, but it would be slow, painful and generally impossible to get exactly the same settings twice. A hardware eq capable of the kind of very narrow, accurately located cuts and boosts Sonar or Logic's channel eqs can do is something I can't do in hardware at all easily or repeatably.
In "effects" plugins I guess I use reverb and compression most. The reverb tends to be Valhalla at the moment, and the compressors that see most use are 1176 and LA-2A types. Cakewalk provide good examples of both, I marginally prefer the Waves 1176, but the CA-2A is a bit better than the Waves' version to my ears.