Here are some suggestions. This idea is so badass that I fully intend to make this army myself as soon as I get some viking minifigs. I know that 4 wanted a character with the last name Umlaut, but that happens to be one of the characters from Guitar Hero. In an attempt to keep a shred of originality, the guitar player's name is based on this videogame rock legend.
Magnus Larson (Those of you who have played guitar hero can probably already picture Magnus)
His name roughly translated means: The great son of Lars (the viking from guitar hero)
Björn Wolff (Mentally unstable and unpredictable, completely out of control. Has a voice that can kill children and other small mammals)
His name literally translates to "Bear Wolf" because I think it's funny. Shut up.
Gunnar Skjeggesberg (A large, armored viking with a very thick beard)
An excellent name for a viking I made up. Gunnar is Norse for "Battle" and his last name is roughly: The bearded one's mountain. Because he's just that metal.
Thor Hjalmar (Beefy and scary looking, wears a giant helmet)
Thunder Helmet, need I say more?
Yngve Bjurbäck (often sacrificed by the other band members)
This name isn't really significant, much like a keyboard in a heavy metal band.
Also, 4 and I had already begun coming up with stats for a rock themed army on the Frappr forums, I'll link the stats he already came up with.
IVHorseman wrote:VOCALIST: spits out cookie-monster-esque death metal lyrics from his throat. causes all minifigs within 1d6 inches to drop everything and headbang until singer stops (his throat gets tired after 1d6 turns).
DRUMMER: always carries drumsticks of death, which are like small melee weapons, except he can use them as if they were rapid fire weapons (1d6 fire rate).
BASSIST: can blow amps to pieces with a funky base line. at will, the bassist can cause an amp to explode in a (size)d10 explosion. can only do up to 2 in one turn.
... and here's the stat card I made that he was talking about before: