I made this last night as a filling for a Devil's Food cake with chocolate buttercream frosting. It went over really really well and was very easy to make. The recipe is enough to frost an entire cake.
Chocolate Mousse Frosting - Recipe - Cooks.com
3 c. heavy cream
1 1/2 c. sifted confectioners' sugar
3/4 c. cocoa powder
Dash of salt
In a chilled bowl blend ingredients, then whip until mixture holds a peak. Refrigerate.