I've been playing on Skyblock for awhile now and I thought I'd share with you my progress :).
The reason why there is a Mob Spawner in one of the chests is because i use the Spawner GUI mod by Risugami.

Features:
- General farms
- 4-Story animal pen
- Slime spawning area
- Mob grinder
- Pigman grinder (for gold)
- Magma cube spawning area
- Cobblestone generator
- Giant mushroom farm
- Bridge to the real world (New Faster Traveling System)
- Snowball generator
- Enderman grinder (Wasn't easy D:)
- Bridge to the real Nether

Things I want to add/finish:
- Nether wart farm

Give me any ideas for thing I can add!

Additional Notes

Mods I used:
- Spawner GUI (http://www.minecraftforum.net/topic/75440-v11-risugamis-mods-everything-updated/)
- Elemental Arrows (Same link as Spawner GUI)
- Nerd-Boys Shield mod (http://www.minecraftforum.net/topic/895339-110-nerd-boys-shield-mod-132-enchantable-shields-now-with-less-im-a-noob-bugs/)
- Treecapitator (http://www.minecraftforum.net/topic/124117-100-daftpvfs-mods/#treecapitator)

Texture Pack is Sphax's PureBDCraft (http://www.planetminecraft.com/texture_pack/sphax-purebdcraft-46664/)

Download the original SkyBlock! http://www.minecraftforum.net/topic/600254-surv-skyblock/

Got the traveling mechanism from: http://www.youtube.com/watch?v=PvWeQlmidt4