Different beer styles traditionally have different carbonation levels (see below), also known as Volumes. The level of carbonation in beer is a by-product of the temperature of the beer and the pounds per square inch (psi) of carbon dioxide applied to it. Carbonation levels will fluctuate if either the temperature or psi is changed.
(Link is dead, try this pdf instead. Chart is at bottom.)
Traditional Carbonation Levels
British Ale: 1.8 to 2.2 volumes
German Lager: 2.5 volumes
American Lagers and Ale: 2.6 to 2.8 volumes
Wheat Beers: 3.0 volumes