Ooh, a recipe thread. Good idea. Here's one I've been doing for years, and I've always got great responses from it.

Coca-Cola Cake
Ingredients
1 cup Coca-Cola
1/2 cup buttermilk
1 cup butter or margarine, softened
2 cups sugar
2 large eggs, lightly beaten
2 tsp vanilla extract
2 cups all-purpose flour
1/4 cup cocoa
1 tsp baking soda

Preparation
Preheat oven to 350ï½°
Combine Coca-Cola and buttermilk; set aside.
Beat butter at low speed with an electric mixer until creamy. Gradually add sugar; beat until blended. Add egg and vanilla; beat at low speed until blended.
Combine flour, cocoa, and soda. Add to butter mixture alternately with cola mixture; begin and end with flour mixture. Beat at low speed just until blended.
Pour batter into a greased and floured 13- x 9-inch pan. Bake at 350ï½° for 30 to 35 minutes. Remove from oven; cool 10 minutes.

While it's still warm from the oven, you can mix up this frosting for the top.

Coca-Cola Frosting

Ingredients
1/2 cup butter or margarine
1/3 cup Coca-Cola
3 tablespoons cocoa
1 (16-ounce) package powdered sugar
1 tablespoon vanilla extract
Garnish: 3/4 cup chopped pecans, toasted

Preparation
Bring first 3 ingredients to a boil in a large saucepan over medium heat, stirring until butter melts. Remove from heat; whisk in sugar and vanilla.
Pour Coca-Cola Frosting over warm cake; garnish, if desired.

Note: Don't make the frosting ahead--you need to pour it over the cake shortly after baking.