Quick Hunter Pet Leveling Tip
If you don't want to bring an under level pet into a raid or instance then finding a spot where there's plenty to kill can be a problem. Personally I like to bring a fully leveled pet into my groups as you won't level one as quick through a dungeon as you would in an area with tons of mobs.
In Wrath the best place to go out just to level up a pet was around in Sindragosa's fall. All the mobs are level 80 and by the time you make a full pass around the ravine they'll respawn.
Now in Cata I've found a terrific place to run your pet for some fast leveling. In Twilight Highlands as soon as you arrive in Highbank just head a bit north to were all the mechanical mobs are and start killing. make your way up and around the coastline and inland. They're high enough level that you can get your pet to 85 in about an hour or so depending, if you just go on a killing rampage and don't stop to loot. I'm on a high pop realm and I don't have a problem at all running into people questing that particular area any more, so it's pretty wide open. By the time you make a full pass around there will be plenty of respawns to continue on.