Couple ideas for new biomes...

I really love the diversity this mod adds. Makes things much more interesting!

Peat Bog - Renaming "Bog" as "Quaking Bog" could allow you to do this. A typical Peat Bog would have some scattered, stunted Spruce, stable mounds of small shrubs and otherwise dominated by sphagnum moss. I wonder if you could make a variation on the "Mud" where the player is slowed down, but to a much lesser degree to mimic the squishy nature of thick sphagnum moss (like walking on overstuffed pillows and blankets!). I use HarvestCraft, and Cranberries spawn in the swampy biomes. It would be pretty cool if you could make your own cranberries or collaborate with the creators of HarvestCraft, since a lot of Peat Bogs will have cranberries. I live in Northern Minnesota, and we have plenty of Peat Bogs to lead as an example.

Glacial Valley - A landscape of exposed rock, gravel and sand left by the retreating glacier. Maybe something that surrounds or borders a Glacier biome? Good place to find materials and sometimes having exposed mineral resources.