My guildies podcast will be talking about leveling 58-80 (so um go listen, okay), and that got me thinking about leveling (which I do WAAAY too much of) and ways to switch it up.
First, the random dungeon finder. It's the only way I like playing my mage, and it really does give you a break. Just, um, have some clue before you zone in. Doing things like giving the healer water (and the tank if it's a pally), or soulstoning the healer, or switching out your tanky pet (or blueberry) for a dps one, it generally sets a better tone for the pug. It may not make things run any smoother, but it does tend to put people in a better mood, plus it starts good habits you'll want at 80.
Second, pvp. I just hit WSG on my shaman and well, I hated it with a burning passion. I dunno if the 30-40 bracket is a bad one for shammies, if low-level elemental stinks in pvp, or if I just have no idea what I'm doing. Probably all of the above. But it was a break from questing, and on other toons I've had a blast in BGs, so try it. Worst thing that happens is that you die a lot, get frustrated, and swear off pvp on that toon. And even then, it might be worthwhile retrying later after you get some new abilities or a new BG unlocks for you. I can't stand doing WSG on my priest (required mobility+disc heals=fail), but Eye of the Storm or Arathi, those are great cause I can pair up with a dps and guard things.
Third, the grind. Not grinding for levels, grinding for other things. Rep grinds, rare drops, mounts, and other shinies. It's not the most fascinating way to level, but you can turn off your brain for a couple of hours and just mindlessly slaughter. Things you might want to consider grinding...
Minipets that drop. Granted this list also includes things like the fishing daily pets, but I can't figure out how to filter it. At least it gives you a starting point.
Rep grinds aren't going to be great till you're in the 50s, really. You can use rep beforehand to decide where to quest, but it's not that useful. But once you're ready to hit Plaguelands and/or Silithus, a rep grind isn't a bad way to level. Slaughter undead or cultists and see your Argent Dawn or Cenarion Circle rep rise along with your XP level. Heck, go from Silithus to Zangermarsh, do some grinding and turn-ins (and read wowwiki) and you could hit Northrend with the sexy title Guardian of Cenarius!
Mount grinds tie in pretty closely with rep grinds, but a mount's better motivation than just an exalted rep, really. Get to 70 and hit up Skyguard or Netherwing if you already have epic flight, or go gather beads in Nagrand for talbulks or get the Cenarion Expedition to love you for a hippogryph mount.
Rare drops, well, those could be many different things. Recipes or cloth farming (yes, cloth isn't rare, but it's useful) or a shiny blue axe that twinks love. Maybe even a piece of RP gear or two.
Fourth, dailies. Yes, dailies. While leveling. They offer a good chunk of XP plus some gold, and once you learn them you can generally burn through them quite quickly. Go help the walrus people in Northrend or run the Isle of Quel-danas. You can even pick up some nice gear and get a headstart on those level 80 rep grinds.
So, go forth and do something other than quest! And do listen to the podcast because I know they're covering far more than I am, and will have more tips too!