This recipe is from Mrsmudrash here on CC and it is absolutely delicious. It's a good crusting buttercream too and you don't have to refrigerate it--remember that sugar is a preservative.
This holds up very well. Here too is a picture of the cupcakes I made with it: http://cakecentral.com/gallery/2277375/simple-cupcake
Marshmallow, Whipping cream buttercream
1 lb unsalted butter - whip for 10 min on high
1 - 7oz jar of marshmallow cream - whip on high for 5 min
1 lb powdered sugar - whip on high for 5 min
1/4 cup heavy whipping cream - whip on high for 5in
3 Tbsp vanilla - whip until incorporated. (I used less vanilla)
This makes a really light amazing buttercream. You can add more heavy whipping cream (the liquid, not actual whipped cream) if you want, depending upon the consistency you're looking for.