When you're in the need of some muscle in the low with the versatility to really shape your sound, take a look at the DigiTech X-Series Bass Driver Overdrive/Distortion. Being part of the X-Series, this pedal comes with a few tricks up its sleeve in addition to the familiar controls for level, tone, and blend.
 
Toggling through the Morph knob gets you three unique effects tailor-made for bass playing: a RAT-esque distortion, A searing TS9 overdrive, and a DigiTech DigiFuzz for a three-in-one tone machine.