The Moog Minitaur is a great little MIDI unit; it is a bit one-dimensional though, but if you're after a Moog bass sound then that's not particularly an issue. You can program it via a PC app and save the sound settings ("patches" or "programs" in synthy terminology) to call them back. (One thing to note is that it is limited to the lower registers, so you don't get the full range of a Taurus, unless you maybe use an octave pedal.)
The Behringer Model D, which is a clone of a Minimoog is therefore also a great bass synth. However, it doesn't have presets, so you have to twiddle the knobs and remember their settings; that said, the left-right panel layout helps you understand the signal flow and synth controls.
I've also got a Novation Bass Station, which has some good stuff in there, but it really needs a PC controlling it.