I like having different beers available also. I like dramatic differences, like an IPA or a maibock (or a pseudo-maibock, like a Dead Guy clone). I've done things like American pale ale, oatmeal stout, and kolsch together. It's great!
I have three or more active taps usually. But if I had two, I'd do things like a cream ale and an oatmeal stout; a pale ale and a kolsch, an American amber and an altbier; and so on.