Haven't tried this recipe yet (anything with an ingredients list feels too much like cooking, and that's something I just don't do), but it looks simple enough. Tasty too, and I don't mean just for the dogs.
Homemade Doggy Ice Cream
Yields: 6-8 servings (1 serving = 1/4 cup)
1 apple chopped up (peeled, cored, seeded, and stem removed)
1/4 - 1/3 c. natural peanut butter
1/2 c. water
1) In a blender, combine all ingredients until smooth.
2) Place in container and freeze until solid (about 5-6 hours).
3) To serve to your dog, scoop up 1/4 c. of the frozen mixture into your pup's bowl. He or she can take it from there.
The above was taken from the blog of one of Popeye's fans (lots of vegan recipes for the human too):