Snailish provided an excellent list, but I thought I'd add in some I like.
I still like Crushbone for 5-15, before heading to PC. Although it's in level 90 revamp mode atm. For beginning if you can get regen and ds buffs, along with skinspike potions, Misty Thicket Orcs crank out exp fast, but personally I prefer alot of the other places Snailish mentioned, particularly CR for the quests for descent armor, if not twinked out already.
For the 40s-50s, I like Velkator's, especially when it's a hot zone. I also have to say how much I like Overthere at the lower levels (15-30), also especially when a hot zone. I like Old Sebilis as well for the 45+ for descent xp, and some great loot as well as tradeskill supplies.
Snailish left out Sunderrock for the 60s+. It may be a bit rough, but by 70 is plenty doable and lots of quests there as well, to add to the xp, and get some descent augs both from quests and drops. Plane of Fire is probably the best xp zone for 60-70, if you can handle it at 60. The zone in kinda bites with all the trees blocking the view and every mob wanders, but generally they're doable at 60, until you can handle moving to C1 or C2 with basically static spawns with even better xp.
I also really like Dragonscale Hills (DSH) Farm camp at 65 when you can start doing the 3 quests there. It's very nice, 'cause if a high level comes along to help, you don't really lose (and will probably gain) xp rate, as they kill faster, and with the quest xp, makes up for the lower amount per kill.
For higher xp zoes, look at
this thread.
Personally, at lower levels, I just go with whatever is convenient and descent xp at the time, again unless I'm in need of equipment, then I stick to places I can get some descent stuff. By the 50s I start looking for other aspects (like faction is the only reason I'd do Dranik Scar personally, as the xp isn't that great compared to other zones in that range, but grouping with someone slaughering for faction there will get you some good regular xp). There are alot of places I go at higher levels not in the other post, simply for items, quests, or what-not and generally the xp is ok, if not good, just not as fast the others I mentioned, unless in hot zone mode. Prime example is Ashengate has quite a few good drops and quests to do.
Yther Ore.