Cake central has a huge cake ball thread How About A Serious Thread About Cake Balls? on CakeCentral.com . Lots of flavor ideas if you're up to reading 76 pages!
Crumble cake into a bowl and add a binder (icing, creamer, caramel, etc). Do not add too much liquid ~ just enough for it to hold together or it will be mushy. Mix together and shape into balls. Our medium scoop is a nice size. You can also flatten the mixture and use a small cookie cutter (I've attached a photo of heart shaped ones I did for valentine's day). Chill, then dip in melted chocolate.