My favorites so far for bass:
Low-mid gain: BJFE BBBOD, Barbershop, Runoffgroove Ginger.
Mid-high gain: DAM Ezekiel, RAT.
High gain/fuzz: Green Russian Muff '94.
DAM Ezekiel is really nice, and it has a blend which is great for bass. If you don't want to use a rotary switch, you can use a toggleswitch with leds always on, and some lower forward voltage germanium and silicon in the other two positions like this http://www.muzique.com/news/diode-clipping-switch/
Experiment with different combinations of clipping diodes, they make a lot of difference. The same goes for RAT, I made mine with a clipping switch: stock/silicon, no diodes, turbo/leds.