Iron Maiden's "Somewhere in Time" was the first cassette that I ever bought as a kid in 4th grade. Love that band and have been lucky enough to see them 3 times live, they put on the best show ever, so if you get a chance to see them please do. Metallica's "Kill 'em All" was the next purchase.
I also do like the newer bands, like Lamb of God, and I also like the death metal scene with bands like Cannibal Corpse, Deicide, and my friends somewhat local band Mortal Decay, they have played the New Jersey and Milwaukee metal-fests a couple of times.
Anything with a great guitar riff and pounding drums is good for me.