You may not be familiar with the South by Southwest Music & Film Festival (website), but it's a very large week long event that attracts almost 2,000 bands, industry people, and tons of fans. Primarily rock and roll, but the list of bands that played is pretty long.
I'm not sure there's anything quite like it anywhere else, to be honest. BFrank has attended for the past couple of years, and I've always enjoyed his updates about the music he's seen.