There are a lot of options to continue to build and enhance your character after you have reached level 70. This is only the beginning...
The Burning Crusade was released in January, 2007. This expansion adds a LOT of content to the game which should keep players busy for a while.

Classic Reputation & Rewards

There are many factions that unlock special items and equipment for your character once you've earned their respect. Here are some examples:
Argent Dawn - The Argent Dawn is an organization that makes no distinction between Alliance or Horde, but instead tries to unite the people of Azeroth in the fight against evil. Check out the Vendor Rewards, Armaments of the Dawn, and Recipes that you can earn.

Brood of Nozdormu - Events have been set in motion that will shape the future of all of Azeroth, as the attention of the Brood of Nozdormu is focused on Ahn'Qiraj, the fortress city of the Qiraji. It is there that those who are brave enough to heed the dragon's call should travel. There are very powerful Quest Rewards and special Signet Rings to earn.

Cenarion Circle - At last, the long watch has ended - the hero has risen, to mend that which was broken, to unite those who were divided. But the true test is yet to come. When the gates of Ahn'Qiraj open, will the mortal races stand united once again and face the onrushing terror. or will they fade silently into the darkness that has risen once again in the distant lands of Silithus? You can purchase Vendor Rewards, do Field Duty Quests, and earn Class Quest Rewards. Learn more here.

Thorium Brotherhood - Adventurers seeking out Thorium Point will find that the dwarves of the Thorium Brotherhood hold great rewards for those who aid them in their never-ending struggle against their former brethren. Check out the rewards here.

Timbermaw Hold - The Timbermaw are painfully aware that they will not last on their own against the corruption of the land; adventurers who seek out Timbermaw Hold in northern Felwood and prove themselves as friends of the Timbermaw will learn that the furbolgs value their friends above all else. Check out the rewards here.

Zandalar Tribe - The Zandalar tribe has arrived on the shores of Azeroth to battle Hakkar once again. Aid them and they will grant you powerful rewards. Check out the vendor rewards here and class quest rewards here.

Darkmoon Faire - Players can earn tickets by doing repeatable quests that they can redeem for special rewards. Check out the rewards here and the buffs here.

Burning Crusade factions coming soon...

B.C. Reputation & Rewards

There are many classic factions that unlock special items and equipment for your character once you've earned their respect. We'll be creating Burning Crusade reward pages in the coming weeks and months.
Reputation Rewards

Honor Hold/Thrallmar
Cenarion Expedition
Sporeggar
Kurenai/The Mag'har
The Bone Wastes
The Consortium
The Violet Eye
Keepers of Time
Scale of the Sands
Shattrath City
The Aldor/The Scryers
The Sha'Tar
Lower City

PvP

Arathi Basin

Champions Hall

Player vs. Player Combat
You have equipped yourself and are at the maximum level. Now it's time to use your experience to defeat other players. Discover Player vs. Player combat! There are various events you can compete in:
Honor System - Earn honor points to use to buy mounts, items, and more
The Arena - Compete on a ladder and earn very powerful items
Four Battlegrounds - Earn special items and honor points
Azeroth Outdoor Pvp
Outland Outdoor Pvp - Some rewards can be gained here
Gurubashi Arena Booty Run
Fight at a special arena in Dire Maul
Player vs. Player Rewards
While participating in Player vs. Player combat you can earn Honor Points to spend on items. To find the rewards Alliance players should head to Champions Hall in Old Town in Stormwind. Horde players go to the Hall of Legends in Orgrimmar. Inside you'll find NPCs with cool things to buy. For the Battleground rewards you'll have to head to the entrances of the Battlegrounds to purchase some of the rewards (Warsong Gulch/Arathi Basin). While we don't feature every item on our site, here's some of the things you can buy:
Weapons
Armor
Mounts
Hellfire PvP Rewards (Coming Soon)
Zangarmarsh PvP Rewards (Coming Soon)
Nagrand - Halaa Tokens (Coming Soon)
The Bone Wastes (Coming Soon) - Combo of PvP and PvE
Alterac Valley Rewards
Arathi Basin Rewards
Warsong Gulch Rewards