What effect do you use the most? I bought an ART ECC primarily to use to decide what kind of effects I like so I can buy appropriate individual units later but now I'll I've realized is that I can find uses in various songs for a lot of different sounds. I think that the one I would be most lost without though would be my flange, I dig that swirl. I have finally found a really practical use for the switchable EQ on my amp though. Heavy flange type effects punch through the mix much better with an extreme W shaped EQ.
Tube Overdrive. I like that little warm raunchy boost you can only get with tubes. I'm so used to my EH BMS I think I would not survive (or just be a little bored) if I didn't have that toy.
Ah wait, and compression is very cool makes clean sound better to me but then It's not really clean is it, Well my signals aren't very clean anyway Damn unique synthed bass lines. (*bump* this is a cool topic, it must live)
Outside of compressors and enhancers like BBE, I have been having a lot of fun with some phasers from my Line 6 Modulation pedal. I even have one patch that sounds a little like a "talk box" type thing. Not really usefull for most music but I love messing around with it