Absolut Chocoholic
Absolut Vanilla
Creme de Cacao
Kahlua
Dip the glass in water and rim it with cocoa powder. One night at a party back when I was in school, I made this drink up, as everyone had to come with a cocktail recipe. It's really sweet, so beware. You really don't know you're drinking something alcoholic because you can't taste the liquor, so these will knock you on your ass if you're not careful. Speaking of which, here's another one that is devilishly good, but dangerous:
Malibu Pineapple
Malibu rum
Pineapple juice
I don't remember how much of each you're supposed to put in, but equal parts sounds about right. And for the above recipe, Malibu Rum is the best to use for that coconut flavor, I've found.