Musicians and music lovers, what's your favorite effect? You can answer either in general terms (heavy distortion, shimmery plate reverb, etc) or specifics (Big Muff, Empress Superdelay, Pigtronix Mothership, etc). I'm thinking in guitar terms mostly (because that's my instrument), but feel free to answer in your own perspective.
For me, it's tremolo. I think it's possibly one of the most underrated effects around. I love a nice subtle trem on blues and surf, and heavy trem on experimental stuff.
Specifically, I'm deeply in love with my new Empress tremolo box. Check out
Andy's demo for a good overview of its capabilities. I demoed a lot of units and this one was the winner by far.