I've been doing the same kind of research, because I have an Ampeg 410 cabinet and and a Tech21 head that are far too heavy to carry and sometimes too big for smaller gigs. My criteria has therefore been that it's 100w (which is suitable for smaller gigs, and the genres I'm involved in) and I can carry (light!). The shortlist has been [b]GK[/b], T[b]C Electronics[/b] and [b]Fender Rumble (100)[/b]. While I'm still waiting to hear the latter, it seems to be a winner among most gigging bassists, not only for it's good sound, but probably mostly because of it being lightweight.
All of these are under the £300 mark and very decent amps. Again, my criteria is based on the weight and the fact that I have the 410 to fall back on for bigger shows. Having lugged around many amps in my time, my advise would be to think about the weight as well... Hope that helps