The Bass POD has gotten decent reviews as a modeler with effects. From what I've heard, the effects aren't very editable without hooking it up to a computer (someone please verify).
I personally have an ART PhatBoy. It's decent, but not incredible. Only the level can be adjusted on the compression/limiter. It also inludes various preset effects combintaions. Again, only the amount of blend can be adjusted. It further has a "growl" feature that sounds interesting on its own, but tends to lose the bass in a mix (for my tastes). The effect may be useful on some song styles.
All that being said, it does a good job for me in that I can get a good bass tone for recording direct.