There are a few that I use on a constant basis, on both modular stuff as well as synths, guitars and whatever.
Evol Fucifier -- the amount of different levels of both filtered sounds, combined with multiband distortion and tape saturation is marvelous.
Earthquaker 'The Warden' -- compressor, but a much cheaper alternative than using more high end stuff. but has a nice quality and range of compression. No sidechain, but I don't use that shit anyhow.
Dr. Scientist 'Cosmichorus' -- Highly effective and versatile chorus pedal. Sounds like heresy, but I like it better than the Roland RE-501 by far
Catalinbread 'Echorec' -- an emulation of the Binson Echorec; I don't give two shits what it emulates, but it certainly is a lovely little delay pedal.
Spaceman Effects 'WOW Signal' -- Technically a fuzz pedal, but has an LFO that adds generously to the sound, overall. the sound of the actual fuzz circuit complements pretty much any synth or guitar I've run through it. Aces.
I'd like to say that I use the Eventide stuff, but I had to sell my Eventide shit a while back; and I mean, it's great -- lush, open, dynamic. If I could afford an Orville, I'd own an Orville.
Saturnworks Pedals makes a reamp box that's 70 dollars. It doesn't require additional power, and is totally transparent. It's a bit cheaper than the Radial stuff, and it's hand-built, well. I use it to run synths through the guitar pedals. It's effective, and keeps the gain differences from causing unwanted mayhem. Some pedals can deal with line-level without issue, some can't. I use this to avoid problems.