Grab...I do an acoustic version of "One" by U2. That song always gets me worked up to. I can't remember how many times I've cried listening to it. It's even more powerful to sing it.

Other powerful ones:

What's This Life For --Creed
Faceless Man --Creed
The Town I Loved So Well
Nothing Else Matters --Metallica
Bui-Doi --from "Miss Saigon"
Let's All Make Believe --Oasis
Storm In The Heartland --Billy Ray Cyrus
Dance On The Wind --Maddy Prior
A' Ghrian -- Shaun Casey