I picked up one of these on a whim
Custom Audio Electronics MC401
I must say I wasn't expecting such a big difference but this really helps with high end tone suck through true bypass pedals and longer cable runs, Lots more string clarity . Plus ahead of my passive DI means I can run into my recording gear and amp at the same time without loading down my pickups.
I'd looked at the Wampler Buffer too but in the end picked up this one since it has the added benefit of a clean boost.
Definitely not as sexy as a good distortion pedal or other effect to mangle the sound but really opened things up for my sound.