What do you do after 80?

I just reach level 80 today with my BE paladin and i am thinking about finding better by grinding rep but idk what faction should i grind the rep.
Beside get gear from rep, what another way to obtaining blue or purple gear in wotlk?
If i use faction tabard, can i still get rep from another faction ?

You will need these 2 reputations exalted to get shoulder and head enchants(this is a must):
Knights of the Ebon Blade
Sons of Hodir

Rest are optional to get some gear or schematic for profession, also for healer or tank specs head enchants.

You can craft some gear or check Auction House, sometimes you can buy some gear real cheap.

You can que Normal Dungons trough dungeon finder tool, to get some gear and some emblems, later in game you can do this on Heroic and rewards are great.

Try to find a bunch of people to play with, find a guild and do stuff with them.

Get AtlasLoot addon, you can just sit in a city and browse all dungeons, sets and quartermasters to see what kind of gear you can get from what and where.