I started reading this list of the Top 529 Eternal Questions in Popular Music, but it got too weird and chatty, so let's do one ourselves, shall we? They started off with these:
How many roads must a man walk down?
What if God was one of us?
Who let the dogs out?
So, here are the first few that pop into my head:
Should I stay or should I go?
Do you really want to hurt me?
What do you want the girl to do?
What's love got to do with it?
Where have all the flowers gone?
What's so funny 'bout peace, love, and understanding?
Ready? Go for it.