I know it's cliche, but Metallica's is so iconic. You'd recognized the logo if it were just the M and A back to back. Nirvana's Dead W*ore also has to be up there. Some other ones I need to mention are the Rolling Stones, TooL, the Dream Theater "Majesty" M, and, of course, the Deathbat. So I'd say all of these are in contention.