Some of this is going to turn into a "favorites" contest. There was a Machine Head Pedals 72 Degrees on Reverb a couple of days ago for $75. Great low to medium drive sound with any amp I own. If I didn't already have two I would have jumped on it. The Xotic RC or AC Boosts are adjustable enough to keep you amp's sound at low volumes and still drive it from light crunch to medium OD. There are also some clean boosts that do a good job if you can try them out with your amp. You have to boost the volume a fair bit compared to unity gain to get the crunch, but if you have an amp that works well at 1 or 2 with the added volume when the boost starts to crunch you're good. If you can build one yourself, guitarpcb Stage 3 is an easy build and cheap as a kit. I also like the slightly older version of the Catalinbread Chili Picosa that has the smalll switch and single knob. The switch is technically for a bass, but it lets some lower guitar frequencies past sort of like the old loudness buttons on stereos.