TAD Range King

Nice little booster from Tube Amp Doctor. There's still a little bit of confusion on FSB over the correct value of the resistors biasing the base of the transistor, but this should work. Schematic and discussion here. If you'd like a fabricated version of this layout, check out the Strider PCB in the store.

Dan Armstrong Red Ranger

Here's a classic circuit from Dan Armstrong–the Red Ranger. It's a booster with a switch for boosting treble, full range, or bass. Original units didn't have a volume control, but it could easily be added to the output.