Taken from 101 Things To Do With A Slow Cooker, by Stephanie Ashcraft and Janet Eyring.
3-pound beef roast
1 envelope dry onion soup mix
2 cans (12 ounces each) cola (Diet soda cannot be substituted)
Place roast in greased 4 to 5-quart slow cooker. Sprinkle with soup mix. Pour soda over all. Cover and cook on low heat 7-8 hours. Makes 4-6 servings.
It worked out pretty well. The recipe is easy enough. I felt like my meat was a trifle dry, but that might be because we left the slow cooker on for too long (closer to 8 hours than 7) or because I didn't put any of the juice on it.
The coke gave it an interesting sweet flavor. I rather liked it.