Minecraft Biomes O' Plenty mod adds 30 new areas, from marsh to mountain
What better way to spruce up your Minecraft server than with a new Spruce Forest? If you've got 99 forests but a Birch 'aint one, you're covered there as well. There's also Tundra, Tropics, Scrubland, Shrubland, Woodlands and Poundland; Savannah, Rainforest, Oasis, Mangrove, no Womangrove, Glacier, Garden, Crag, Bog and however many more is needed to hit 30. Phew.
Biomes O'Plenty, no relation to the Kingdom O'Magic, comes from one of the developers of ExtraBiomes XL - so you may spot some simularities. It's a simple installation, with no real options - if you don't like part of the world you get, the solution is to keep walking past it until the whims of random seed generation match your own. Check out plenty of pictures here, and grab the mod right here.