The Bad Monkey is a tube screamer clone with a bass knob; for me it did 95% of what the TS9B did for $50.It really hasn't gotten a whole lot of praise or love on the TB forum, but I'm a pretty big fan of my Ibanez TS9B. That's exactly what I use it for. A subtle bit of overdrive.
The Pork Loin and Green Rhino are for guitar, but work great on bass.
The Fulltone OCD is an awesome pedal, very flexible and musical, a real bargain at $130 at GC. And search online for the lowest advertised price as GC will price-match, you can probably get it for more like $120.
And someone will probably sing the praises of the SansAmp VT character pedal- that one gets lots of love, although I have never tried it personally. Especially if you dig that Ampeg sound.