I'm going to have to vote for the theme song. It's winning.
Funny songs: "Building a Supercomputer", "Our Movie's Better..."
Good-sounding: "One Good Scare..."
As another category, the song "Set the Record Straight" is so adorable!
So many ear worms to choose from! I do love the Baljeetles, Little Brothers, Carl's Theme Song and Doctor Coconut, but if you're going to make me choose just one, it's going to have to be SIMP Squirrels In My Pants.
Of course, this is Nerdfighters, so my final answer is Squirrels In My Pants... In Your Pants.
I'd like to think the two aren't mutually exclusive :P but I have to say it's a three way tie between There's a Platypus Controlling Me, Brand New Best Friend, and the extended edition of the Perry the Platypus theme song
I think all the songs are both funny AND good.
I like " I've found a brand new best friend" with Dr. Doofenshmirtz and Dr. Doofenshmirtz. It's always in my head, and is really creative and funny.
SIMP (squirrels in my pants) BEST SONG EVER!