Scout - The Final Countdown by Europe
I picked this because it fits the rush that usually comes off at start and usually the crazed attempts by scouts to force rounds into overtime.
Soldier - Hammerhead by the Offspring
Cmon' it's the soldier, of course it fits.
Pyro - I don't Want to Set the World on Fire by The Ink Spots
Odd choice I know but Pyro is more of a fun-loving class. At least I didn't pick the obvious Through The Fire and Flames by Dragonforce.
Demoman - Drop the Bombshell by Powerman 5000
An explosive song for an explosive drunk.
Heavy - Iron Man by Black Sabbath
He IS The Iron Man
Engineer - Ghost Riders in the Sky by Spiderbait
If this doesn't make you want to ride a horse and wear a cowboy hat, nothing will.
Medic - Hellion/Electric Eye by Judas Priest
Any good medic knows everything about his teammates, where they are and who needs him most.
Sniper - Freebird by Lynyrd Skynyrd
Snipers tend to start off slow, but once they get into their groove, expect a lot of quick kills.
Spy - Enter Sandman by Metallica
This one speaks for itself.