Instant spawn skeletons in Altdorf
At the docks in Altdorf there were a bunch of skeletons, after I killed em they pretty much instantly respawned. I have no way to check if they give XP (i believe they do though, as they are a part of a PQ) (not in range of any of my characters) but they are level 10, and I have no doubt that if they do you could put up and AoE team and do insane amounts of XP \ H there. They do drop loot.
Just run along the docks and look for the skeletons if you feel like trying it. =)
Ah, and they do give acheivement points. I got one for killing skeletons while I was playing around there.