they make special chocolate for melting (its thin quarter size pieces)but any will work, you might have to add some vegetable oil to thin some types of chocolate out though.
I have my own mini one which is great but also used a big commercial one when i worked for a catering company. We just had a big box of wooden skewers and then marshmellows, cut up bananas, strawberrys, pineapple, and graham crackers.
If you are using a big one do not set it up outside if it is windy or in front of a fan/ ac vent (huge mess). it is a bitch to clean the fountain out after, but IMO its worth it.
Chocoley Just Melt It! - Chocolate Fountain Tips & Tricks I havent used their chocolate but it has lots of ideas for stuff to dip in it and some other good stuff
I need to find out if Nutella can be put in one of these fountains.
But only because Nutella is nasty. :)
Oh, and just so you don't think I'm going to just come in here for a drive-by, here...
Is it safe to use Nutella in my Chocolate Fondue Fountain? If so, how? - Yahoo! Answers
Oh snap. I done got told.