This came up at work the other day, and I started to think of songs that sound really really alike, and heres what I got so far:
Puddle of Mud - She Fucking Hates Me and REM - Stand
Jet - Are You Gonna be My Girl and Iggy Pop - Lust for Life
Offspring - Why Don't You Get a Job and The Beatles - Ob-La-Di, Ob-La-Da
Anyone got any more?