I really like Not Your Mother's Slow Cooker Cookbook. It has real recipes, not recipes that consist of adding canned soup to meat or vegetables. I highly recommend it.
You can easily adapt many regular (non-crock pot) recipes to be cooked in a crock pot, and vice versa. Stews, soups, and chilis are the easiest to adapt.
I recently made an Eggplant and Chickpea Strew recipe that was delicious. I cooked it on the stove instead of in a crock pot, but the original recipe is written for a crock pot. Here it is if you're interested: