At our house, a favorite is chicken, on the bones or not (it will fall of if it is on the bones), potatoes, carrots, celery, cream of chicken soup and seasonings. Put it on low for 10-12 hours and it's delicious.
But you can throw just about anything in it. There's a recipie for crock pot chicken and dumplings somewhere that's delicious...and the pulled pork is amazing. Chirstmas lunch last year because you could get some whenever you were hungry after my dad grilled steak.
http://busycooks.about.com/od/chicke...ckendumpli.htm but I suggest putting some of the liquid in a pot and boiling the dumplings that way, our crock pot doesn't bring it to a high boil that fast