There's an intro/riff from Pennywise which I really like playing, it's called God Save The USA. It is pretty easy but it is really fun to play.
e ----------------
b ----------------
G ----------------
D 5~------5~-----\
A 5~------5~-----\
E 3~------3~-----\

Then: [Play this bit fast]

e ------------------
b ------------------
G ---3---3----8---8-
D 55-3-3-3-55-8-8-8-
A 55-1-3-1-33-6-8-6-
E 33---1---33---6---

e ------------------
b ------------------
G ----88-8----------
D 55-588-888-8101010
A 55-566-688-8101010
E 33-3----66-68-8-8-



I also like playing Metallica, Living End, Guns and Roses, RHCP and SRV riffs.