You can totally cook ground beef in the crock pot. Yup.
Go ahead and buy that giant thing of ground beef, plop it in your crock pot, and turn it on low for 6-8 hours or until cooked medium well in the center (you'll finish browning it when you go to use it in your meal). The grease and moisture will mostly cook out, surrounding the ground beef in liquid that you can drain off, leaving you with more or less a roast of lean ground beef. Break it up or slice it and put it in baggies or freezer-friendly containers and freeze.
My shepherd's pie took all of 15 minutes tonight! I browned up the thawed ground beef in a big pan (and didn't have to drain it!), tossed some frozen corn on top right in the pan, covered it with creamed corn and instant mashed potatoes, heated it through, and - DONE!