As far as I can tell, band names are typically treated as a plural if the name of the band starts with "the" and is a plural noun or based around a plural noun -- or more generally, if it seems to be referring to its members as a collection of entities -- and a singular otherwise. So we would have:
- The Beatles are a great band.
- Korn is a great band.
- The Rolling Stones are a great band.
- Metallica is a great band.
- Led Zeppelin is a great band.
- Nine Inch Nails is a great band.