...then Iskatu farm is still good. Or at least it was, pre 1.0.3. I was 58 on my monk when I killed Diablo on hell, and still needed to grind something to open up inferno. I went to test out several zones of act 3, Azmodan too, and then ended up doing Iskatu in act 4. Noticed the XP he still gives from the quest is pretty insane for the time it takes to kill him. As a comparison, the Rakanoth quest gives like a third of what this quest gives.
The quest (Fall of High Heavens) gives you 60000xp, Iskatu himself gives you 17825xp (plus any +exp after kill and helmet gem), for a total of 77825xp (before modifiers). The quest also gives you 1280g and Iskatu himself drops around 200-800 gold (0% gold find), as well as 2-3 magical items, for a nice 1500-3000g per kill.
It took my monk some 60-70 seconds to do one run; select the quest, start game, run to Tyrael, TP then port back (to skip dialogue), talk to Tyrael, Esc twice to skip dialogue, enter portal, Esc Enter to skip the cutscene, kill kill kill, grab stuff, TP, leave game.
59 to 60 takes 2250000xp, so if you do the entire level using this method, it'll take you a total of 29 runs, which will take you a bit over half an hour. This will also net you a cool 60K in gold as well as some crafting materials and potions.
I know this may come as no surprise to most of you people, and is old information. In fact I think there may have been a thread from a while back, but I couldn't find it, and since bumping old threads isn't allowed I thought I'd make a new one. I mean, this was my fourth 60 and I still made the mistake of going out to the zones myself, so I thought I'd save someone else a bit of time by pointing out how good this guy is still for exp. The difference between doing Iskatu runs and killing throngs of monsters in act 3 was huge. Although, I only had like +11xp per kill at this point, so that might make a difference. By doing these runs you don't have to waste any time looking for monsters, though.
As I said earlier, this was done before the nerf patch, and the servers just went down here in Europe, so I don't know if this will change.
This is a solo method without any "join a game and get a quest without doing anything" -tricks. You start a quest, and kill an opponent with at least some difficulty, for lower geared people anyway, so I for one think it's a very good and legit way of getting fast XP.
Oh and also, I know about the "too many instances" -limit they're imposing, but you can just play up until that limit then, and go do public games after that.
In any case, I hope this thread helps someone.