I was going to post my Dump Cake recipe, but it's identical to Milissa's!

You can frost it with Cool Whip if desired, but personally I prefer it unfrosted with vanilla ice cream. It works with either a white or yellow cake mix. I have read recently on a recipe site that you can use the same recipe with a chocolate cake mix, but I haven't tried that variation yet.
Here's a good one:
MICROWAVE CAKE
1 (18.25 ounce) package cake mix
3 eggs
1 (21 ounce) can pie filling
1/2 cup applesauce
1 Mix the box of cake mix, eggs, pie filling and applesauce till moist. Use a microwave safe bundt pan or substitute a microwave safe bowl that has a microwave safe cup or cone placed in the middle of it (to mimic a bundt pan). Pour mixture into the bowl around the cup.
2 Bake on high for 6 minutes 30 seconds, turn and bake for another 6 minutes 30 seconds on high. Remove from oven and cover bowl with a dish and let stand for 5 minutes (this finishes the cooking process).
3 Turn cake over onto dish and remove cone (cup) for a delicious quick dessert. Good hot with vanilla ice cream or whipped topping.
You can use any combination of cakes/pie filling, ie: apple with yellow cake. I've done this one with chocolate cake & cherry pie filling, served warm with chocolate syrup & ice cream... almost like a black forest cake, but less work! This one did come from allrecipes.com (Sorry, Sara, but it's a good one, I promise!). Another reviewer suggested using spice cake and pumpkin pie filling, which I haven't tried, but it sounds good!