[primem0ver one biome which I have not seen mentioned is Temperate Rain Forest.
The temperate rainforest is not considered a biome as it is a feature of several biomes though I would agree it should be were it not for the different types that exist, Temperate rainforests (of slightly different types) are found in Humid Sub-tropical, Humid Continental, and the Biome I am calling "Cool Continental" (an unofficial title I have given the Dfb Koppen Climate).
The problem with these three climate types in the Koppen system is that they are really divided into separate sections, each of which could be considered its own biome (which is why I am subdividing biomes into coastal, inland, highland, rainshadow). East of the Mississippi, the US continent would be one giant forest were it not for civilization. At one point in US history, it was rumored that a monkey could travel from the Atlantic to the Mississippi without ever touching the ground. That would probably still be true were it not for highways, though the path taken would have to weave around our cities.
The biggest cause for the change in vegetation is the Appalachian mountains. They provide a barrier to a lot of moisture but not enough of a barrier to cause a rain shadow (because they are not high enough in elevation). Another reason for the lack of rain shadow is the Gulf of Mexico.
West of the Appalachian's the number of trees lessens noticeably until you get to the Mississippi at which point they quickly disappear as you travel further West. Yet the Humid Continental/Subtropical Biomes reache all the way through most of Kansas, Iowa, and Oklahoma where most trees are found only along rivers and where the groundwater reaches close to the surface (except in the Ozarks... because the higher elevation causes condensation of the remaining moisture).
But while some (including me) might argue these forests should be a separate biome (much like tropical rainforest and the monsoon climates are separated), the Koppen system does not separate them out, partly because they of the subtle differences in between tree species between the three climates that still exist in their western reaches.
Sorry... I guess I tend to be a bit too informative at times
