Mussels are soooo easy.
I'll post up something more elaborate later, but I like to drop them into already made (sometimes my own, sometimes organic jarred sauce) spaghetti sauce, then serve with pasta.
To cook them, I put about 9 or so mussels into 1 cup of liquid. A nice mix is 1/2 water and 1/2 white wine. Bring to a boil, then simmer a few minutes until the shells open. Discard any that don't open, then either be arty and arrange the open shells on top of the pasta or, like me pull out the meat, then stir 'em in. Simple and adds a nice shot of protein.