Best way I've found to deal with a banjo is with a shotgun....
Oh, you meant mics.
I usually reach for my MG M930s. Seem to work pretty well for most players. I'll usually put it through either a good colored transformer based pre- API and A Designs are usually the first place for me to look.
One of these days, I'd like to give the Sennheiser MKH 8040 a try. I think it would probably work mighty well as well...
--Ben