You might be thinking of the Audio Technica AT4033. That's the mic bluegrass bands traditionally favour, in a 1-mic-for-the-whole-band sense. It's a large diaphragm condenser mic. Quite bright and cutting, but with plenty of bass and body if you position it right.

When I saw Chris Thile play solo at the Borderline last year, he used one AT4033, positioned half way between his banjo and his mouth (about chest height). It sounded perfectly balanced. (If just slightly bright).

UK residents might be interested in this scheme Audio Technica are currently running: http://eu.audio-technica.com/en/support/firstimpressions/
I used it to audition a few mics and concluded the AT4047 was the perfect mic for my Django guitar.

Kara - your instincts were in some ways correct to single out that Oktava mic: it is indeed a very, very good instrument mic for acoustic instruments. But I wouldn't use it in a live situation, simply because it requires phantom power.

I would buy an SM57, as others have suggested. You can't go wrong with it. However, if by any remote chance you dislike it you can sell it off again for not much less than you bought it (they are that cheap, it's irrelevant).

Alternatively, Shure also sell the 545SD, the retro-looking precursor to the SM57. This mic sounds slightly darker to the 57 in some contexts: particularly on male vocals (it's a good mic if you ever want to thicken up a male or female voice).