I read a cookbook that suggested you add 1 cup fresh raspberries to your pan of peaches when making a peach crisp recipe. I tried it and it adds a tartness to the sweet peaches that I really like. I also liked that the recipe suggested using some brown sugar instead of all white. I'd give you the recipe except that I didn't really like the topping part.
I've also read that you can do the same thing with an apple pie and that it will turn out very yummy! Don't you love it when all of these delicious fruits are farm fresh?