For a baking beginner, what cake icing you recommend? I am a beginner in cooking/baking.
I have tried a couple of cake and muffin recipes, the simple ones turn into a hard crust after a while.  

There are good ones that need temperature measurements and are complicated for me to make like  "Cake Decorating: How to Make Buttercream Icing" http://www.youtube.com/watch?v=n9xIxBbocYI 

Is there a simpler one that a novice can make, for general cake or muffin icing?
Buttercream is pretty simple, start with room temperature butter, beat it until it's white, slowly add icing sugar, add small amounts of milk as needed to keep the consistency right.  

For each 1/4 cup (1/2 stick) of butter, use about 1 1/2 cups of icing sugar (sifted) and 3 Tbsp of milk.  You can do it in a mixer, a food processor, or just use a bowl and a whisk.  I used a whisk a few days ago when I realized my large stand mixer is overkill for the small amount of icing I wanted and I found that microwaving the icing for about 10 seconds helped me stir in the sugar when it was getting too thick.