There is one alternative that noone has covered yet, but it's not possible until around level 60. I'm talking about full blown raid leveling. I haven't seen the scaling of xp in raids lately, but I remember back in the day raiding Zul'Gurub with a level 59 mage. I got like 20.000 xp for the whole instance (not a lot yeah) if my memory isnt completely washed.

But I'm not thinking about raid instances right now, I'm thinking about the super elites in Blasted Lands and Winterspring. If you remember the old Kazzak thrash mobs, scaled for 40 man raids. At some point when I was leveling my shammy team I went to Blasted Lands just to check out if it was possible to grind those. They were riddiculously hard, but I managed to kill one mob. Thing is, I can't remember what level I was when I tried this. With 26 guys, you should be able to grind those pretty smoothly, but I wouldn't even think about it until at least level 58. The elites in winterspring was not so hard, I remember soloing those at level 60 (singleboxing a hunter) and selling the priest epic questitem on AH for decent prices, but the elites in Blasted Lands is probably among the hardest non-instanced "generic" mobs in the game.

http://www.wowhead.com/?npc=8717#comments <--- This is one of the mobs I'm talking about. Should be fairly easily soloable for a level 70 character of any kind, the question is whether or not they're grindable at say level 58-60, with a decent xp reward.