I have the 360 version !
The 360 version gets all Skyrim DLC 30 days before other versions, so you lucked out.
Dawnguard - adds about 20 hours of content (story/quests), crossbows, mounted combat, (a really awesome transformation that I won't spoil for you), your own castle (if you make a choice), new shouts, spells, dragonbone weapons, a new follower, basically pick this up immediately if you seriously get into the game.
Hearthfire - adds 3 new homes you can build from the ground up + the ability to adopt children. Pretty neat stuff but not necessary/nothing too special. Pass on this one unless you just want as much content as possible (I enjoyed it).
Dragonborn - this is the one that comes out in 2 days. It adds about 20-30 hours of content (story/quests/island to explore), it adds multiple new houses to buy, it adds a new follower and romance option, it adds new armor, weapons, ability to ride dragons, new shouts, etc. Basically, buy this one too (but from what I understand, it's best you beat the main story of the core game first).