Derwood's list:
Tool: a fine and innovative band
Radiohead: A band which I despise to the core of my being for no reason I can pin down
Glassjaw: One that sounds like it might be worth giving a listen
Opeth & The Darkness: First I've ever heard of them (though they might have been in a thread and, because I've never heard of them, I just scanned past)
Godspeed You! Black Emperor: Nothing I want to bother with.
Aphex Theory: I heard they have an interesting video
A Perfect Circle: Tool, Part 2. Good, but I like part 1 better.
Dream Theater: Overly melodramatic, but insanely talented. A good listen.
Dashboard Confessional: Never had the urge to listen to them.
GOT's addendum:
The Beatles, Led Zeppelin & Rush
I think you have to have listened to these to be an adult, able to vote and drink.
One that keeps popping up: The Mars Volta. I haven't heard anything yet, but I am looking for it.
And, of course, to be truly cool in any context, you have to love <b>Blue Öyster Cult</b>. It's just the way things are.