First and foremost, you can do a bunch of new dailies. There're many new dailies wow power leveling throughout Northrend, starting at level 71 and going up to level 80. They are all good ways to get wow gold and great ways to boost your reputation fast and efficiently.
   Places like Icecrown Glacier are loaded down with multiple options for end-game content including instance progressions, though it is not yet in place for you to actually play through, but you can play through most of the build up to Icecrown Citadel. There are tons of rewards, great lore involved and lots of ways to get into both Player vs. Player and instances in this segment of the game.
   Secondly, you can do raiding, raiding and more raiding as you want. It is for sure that there are raids and dungeons you can run at level 80 as well. At present there are four raids to play through such as Naxxramas, Obsidian Sanctum, The Nexus, and the Vault of Archavon. In the end, you'll be able to get through a whole lot of content and then you can run through all of the level 70-80 instances again in heroic mode. Expect new dungeons and raids to be added as the game ages as well, with probably another two years between now and the next expansion pack.
   Thirdly, you can improve Player vs. Player. The Player vs. Player content has never been a strong point in World of Warcraft, but this release brought quite a bit of new content to enjoy, if you know where to look for it. This includes Season 5 Arena play, the new Player vs. Player daily quests in Grizzly Hills, the new battleground, called Strand of the Ancients, and the new outdoor PvP zone, Lake Wintergrasp which offers some of the best PvP rewards in the game.
   Lastly, you can rack up the achievements. When you have nothing else to do, start getting some of the nearly 1,000 achievements in the game, building up your character and your profile to showcase all of the amazing things you've done that others have not. Get 100 mounts, defeat everyone on heroic and explore every continent. The list goes on and on as there are tons of these to do.
   As above mentioned, you have learnt that there are a lot of things to do at wow power leveling level 80. You will not ever feel like you are out of things to do at level 80 again if you are really smart. There is a shortcut you can take is that you can visit the Warcraft Formula site and learn how other level 80 players are enjoying all the new end-game content.