Be warned, it's not the typical alternative rock that I am known to listen to. It's emotional, well written harder rock (some may even call them emo, though I think they're closer to metal), with amazing guitar work and vocals.
Here is a Wikipedia article to read if you want some interesting reading:
http://en.wikipedia.org/wiki/Coheed_and_Cambria
Welcome Home, with it's constant (almost Led Zepplin-esque) beating guitar and drum has become one of my favorite songs to run to. "A Favor in the House Atlantic" (also called "Good Eye Sniper") is also one of my faves.
Where else are you going to get lyrics like this:
"Always and Never":
If beauty sits the child's kiss
Of laughter I amend
Can you catch her if she runs?
"Wake Up"
I've earned through hope and faith
The curves around your face
That I'm the one you'll hold forever.
If morning never comes for either one of us,
Then this I pray to you wherever.
"The Suffering":
Listen well... will you marry me?
Not now, Boy
Are you well in the Suffering?
You've been the most gracious of hosts
You may be invited, girl, but you're not coming in
If you are a fan of complex musical arrangements and great lyrics, you may like this band. Check them out. Here is a pic:

I am going to go finish rocking out.