Pro Tone Pedals has released the Low Gear Thruster bass booster pedal which provides up to 20db of clean gain specifically for bass guitar.

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From the Pro Tone site:

A very beefy sounding booster, for bass guitar, this single-transistor power booster will give bassists unprecedented powers of tone and warmth. From jazz to country; surf to metal- this is the baddest bass boost of them all.
The Low Gear Thruster features:

Durable aluminum housing with an enamel finish
True bypass switching for tone preservation when not in use
Point to Point construction
Operates on a standard 9 volt battery or BOSS style adapter
Hand built construction- built in Texas, USA

For more information and pricing, see: http://www.protonepedals.com/