Boober, Cantus, and Cotterpin.
Those are my two favorites.
Boober because I find his eternal pessimism adorable. ;P
Cantus because I LOOOOOVE how he talks! XD
And who doesn't love Cotterpin?
I was particularly fond of this one part in "The Cavern of Lost Dreams" when she's begging Gobo to help her find it, and she flings herself to the wall saying "I'm DESperate!" XD