Probably the easiest basslines are in rap and hip hop songs, still catchy though, wish i 
have an effects pedal to make it sound cool :)
Eminem has some catchy bass lines though, always good ones when you play
basically it's this:

G|---------------|
D|-----3-3-----5-|
A|-3-56---6-65---|
E|---------------|

REPEAT FOR WHOLE SONG! (If your not bored by the end ;) )