Lots of great recommendations on here. Tone Bender is a must-have, IMO. One under-the-radar fuzz that's definitely worth a look is the If 6 Was 9 from SolidGoldFX. As the name implies, it does a mean Hendrix - but there are a hell of a lot of other killer tones in there, too. A lot more versatile than a lot of other "vintage style" fuzzes out there.