What temperature should I serve my beer? In general, what's the best way to work out the temperature at which to serve a particular beer? Room temperature? Cold? Supercold? Warm?
It depends on the beer really.  A good rule of thumb is darker beer should be served at a warmer temperature than lighter beer.

For instance if you refrigerate all of your beers and then pull them out of the fridge and drink them instantly you will miss A LOT of the flavor complexity of pretty much every stout and porter you put to your lips.

But, if you let the dark stuff warm up for just 15 minutes before you drink it (let it sit at room temp) a bunch of new flavors will appear that you never would have noticed otherwise.

This doesn't work so well, in my experience, for lighter beers like pilsner, lager, or hefe-weisen.  They really are meant to be drank cold and letting them get warm changes their flavor profile for the worse.

Obviously there will always be personal preferences but, at a minimum I encourage you to try letting your darker beers warm up just a bit and see what a positive difference it makes.

Here is a temperature guide from this article: Serving Temperature Guide. It categorizes different beers based on temps to serve at.  These are basic rules of thumb and again you'll want to experiment and discover what temps you like your beers at the best.