Hmm, let's see.
I just got an ISP decimator yesterday, but it's already becoming my favorite "effect" (why did it take me so long to try these? So easy, so effective, so transparent

)
Eventide pitchfactor. It's insane what this thing can do. I use it for detune, for my delays, as a tuner, to make weird synth noises when I want, as a harmonizer when I feel like being Dave Murray AND Adrian Smith (and sometimes Janick too) and I'm barely scratching the surface of what it's capable of. And it has MIDI capabilities, more pedals need this (But they need to put the MIDI jacks on the top, not the damn side where they require me to keep this pedal four miles to the left of whatever comes before it in the chain so I can plug in the MIDI cable that goes to my amp

)
Digitech Whammy. I actually prefer the whammy mode on this to the pitchflex on the pitchfactor, it has that great melting computer sound that other pedals are just too well designed to reproduce
Digitech Hardwire Reverb. My favorite pedal reverb. I like it better than most sub $400 rack reverbs too
Hmm, getting tough to pick a fifth. In terms of what I've had the longest it's
the Guyatone MD-3, but that's homeless since I got the pitchfactor. My fifth place I guess comes down to a tie between the basic
GCB95 crybaby and the Ibanez WD-7. I've gotten more use out of those two pedals than any boutique way I've had, and I got them for a combined price of under 150 bucks. I am pretty eager to try out the new Jerry Cantrell wah though.
TL,DR