This is from Jackson's "Beer Companion":
* well chilled: 45°F for pale lagers
* chilled: 46°F for wheat beers
* lightly chilled: 48°F for dark lagers, altbiers, and German wheat beers
* cellar temperature: 55°F for most British ales and Belgian specialty beers
* room temperature: 60°F for strong dark ales and barleywines
I think most beers taste best in the 50-55 range, including most good American beers. British styles I go a bit warmer.