I have tons and tons of fav Fraggle songs, but here are some off the top of my head (and a few that haven't been mentioned yet!):
Follow Me
The Friendship Song
Pass It On
Catch a Tail by the Tiger
Lost and Found (omg the yodelling on this one is the definition of awesome)
Pass It On
Get Goin' (LOVE it)
Bad News (the way Boober screams "all day" and "all year" is terrific)
Bring Back the Wonder
Only Way Home (sometimes I find myself walking home from the train going 'lalalala lalala la la laaaa' etc haha)
All Cantus, all the time (and I LOVE Steve's solo in Music Makes Us Real--he does that really well, IMO)
Pukka Pukka
...
I could kinda go on and on, so I'll leave it there.
Oh, but someone mentioned Wembley, Wembley Number Nine, and I just have to say that every time I hear Boober say "sugarlips" I pass out laughing. No joke. Well, maybe a little one.