If you like the Fuzzrocious stuff, whilst the Rat-Tail can do low gain, it shines on high-gain. I'd look at the BDPG, Demon or Dark Driving.
Xotic BB Pre does a real nice low-gain.
The first Guv'nor is cool on bass, supposedly what Timmy used on the first RATM album, 2nd Guvnor....I've not tried.
Catalinbread SFT also gets a fair mention from many people.
Theres a LOT out there, your ears are very different to everyone elses, so just experiment with as many as you can
Si