At first I thought that this would be hard to name five, but after skimming through the thread I can barely keep it to five.
Cheers - Where Everybody Knows Your Name
Friends - I'll Be There For You
Scrubs - I'm No Superman
The Golden Girls - Thank You For Being A Friend
The Big Bang Theory - Big Bang Theory Theme (real imaginative name there)
Can we count closing songs? Throw in Red Dwarf and Frasier to replace the bottom two.
I don't know why all my songs are for sitcoms either, as I have plenty of songs I liked for dramas too.