We don't really like sauces on things, and the basic steamed Brussels with just butter and some Kosher salt are perfect for us. ** If you "steam" them in the microwave, your house won't smell like cooked cabbage. Also, they're much healthier that way (since the vitamins won't leach out into the water, like it does when you steam them on the stove).
Wash and just barely trim the stem end of each Brussels sprout. The most important thing to do is to cut an X into the bottom of the stem end (see 2nd photo). That way the thicker stem will cook at the same speed as the top. Then stand them up (x stem end down) in a microwave-proof dish. Put about 1/4" water in the bottom.
I dot them with little pieces of butter, and give a sprinkle of Kosher salt on top (but you can do this after they're cooked, if you'd rather). Cover, and microwave on HIGH for about 4-6 minutes (depends on your microwave ~ how many Brussels sprouts you have, and how big they are). Toss in the melted butter and serve. ** They should be slightly al dente (you may need to cut larger ones in half with a knife when you eat them), and the color will be a beautiful bright green. (If they're soggy or olive green, then they're over-cooked)
TIPS: Leftover Brussels sprouts can be cut in half, or sliced and mixed with sliced radishes and a tangy vinaigrette for a wonderful salad.