Outland Reputation Battlegear
These introductory level 70 sets will help boost your gear as you enter endgame battlegrounds and get your feet wet in the arenas. The pieces can be purchased by becoming honored with Cenarion Expedition, Honor Hold/Thrallmar, Keepers of Time, Lower City, and the Sha'tar. Which faction has the piece you need varies from set to set, but for the complete set you must be honored with all five of these factions.
By the time you reach level 70, you should be well on your way to honored with these factions, and need to become honored to get your Heroic dungeon keys, anyway. The entire set costs less than 150 gold. Since everyone reaching level 70 has access to them, they may be among the most important sets in the game.
Pieces from this set will be replaced with honor and arena gear, but by picking them up as soon as you reach 70, you will drastically up your stats and Resilience.
The links below present the gear stats and which faction you must have for each piece:
Druid (Feral): Dragonhide Battlegear
Druid (Resto): Kodohide Battlegear
Druid (Balance): Wyrmhide Battlegear
Hunter: Stalker's Chain Battlegear
Mage: Evoker's Silk Battlegear
Paladin (Holy): Crusader's Ornamented Battlegear
Paladin (DPS): Crusader's Scaled Battlegear
Priest (Holy): Mooncloth Battlegear
Priest (DPS): Satin Battlegear
Rogue: Opportunist's Battlegear
Shaman (Enhancement): Seer's Linked Battlegear
Shaman (Elemental): Seer's Mail Battlegear
Shaman (Resto): Seer's Ringmail Battlegear
Warlock: Dreadweave Battlegear
Warrior: Savage Plate Battlegear