Let's be honest here, rogues don't really need a leveling guide. We simply continue to exist, as we always have, leaving a trail of the dead in our wake. We're trained killing machines who also have the ability to Stealth around to avoid detection. With Recuperate, we never need to stop and eat, and with Deadly Momentum, we never need to stop and Recuperate. Basically, if you want to level your rogue from 80 to 85, just find any new zone and start killing anything in sight.
After questing your way through Cataclysm's new content, you've reached level 85. Unfortunately for you, much of your old gear is now quite out of date. Think of Azeroth as a giant piñata filled with loot, and then imagine Deathwing's entrance into the world ripping a hole in said piñata the size of the Maelstrom. There are reputation vendors dying to give out new leather gear to anyone loyal to their cause, and new dungeon bosses mean new dungeon drops. The best part of all this new gear is that with the new armor specialization system, hunters and warriors will finally stop rolling on our leather.