I wish to call attention to the wonderful thing that is Biomes O' Plenty, which is something made by one of the previous ExtraBiomes XL mod team members.
http://www.minecraftforum.net/topic/...ebration-v040/
It's also compatible with Forge, and from reading a bit in the thread, it seems it is possible to tweak the configs a bit to actually get both ExtraBiomes AND Biomes O' Plenty working together.
That's a fuckton of biomes. Biomes O' Plenty has a lot of very very dramatic biomes, and it seems to do some very curious things with cave generation in its numerous mountain biomes. Been playing on my personal server with some guildies and creating a mighty dwarven fortress in the Alps biome.