[Striiker]

Level 4-6 Qeynos Hills: There are various giant bats and some wolves to kill but the main attraction are the Gnoll watchers and Gnolls. You get great faction for killing them but their most valuable resource are the gnoll fangs. Turning these in to Capt. Tillen in South Qeynos (overlooking the arena) or in Halas to a female Barbarian, Lysbith in the Halas pit (warrior guild) yields exceptional experience (best by far!) The advantage of making the run to Halas is that you get much better coin and stuff to sell.
You can also head down into the Qeynos Aqueducts to kill gelatinous cubes and the named Cubert. Cubert sometimes drops a tattered dress which you can turn in to the guy standing next to the bridge near the bank in South Qeynos for a reward of a +3 Int gold stud earring. I stayed until I got two for each of my Int casters.

Level 6 - 13 Black Burrow: Once again, the gnolls are running rampant in this zone but so are the players who are in search of the gnoll fangs! I recall leveling from lvl 4 through to level 6 in one turn-in of (i think) 8 fangs.

Level 12 - 16: West Karana: Head to West Karana to the old Miller's farm where you will find many scarecrows wandering the field. These require magic weapons to hit them though. Beware of the occasional roaming werewolf and the Ghoul Messenger who like to wander past this area. There are also grizzly bears, giant spiders and wisps to kill around here.
I also headed to Erud's Crossing (aka Wisp Island). There are numerous wisp spawn points. I made some serious plat due to the light stones and greater light stones which the wisps drop. (Turn in the GLS to one of the gypsies in North Karana and then sell the book which she gives you back for about 10 PP each). The downside is that if you get adds, you will die as there is no zone line here (boat / translocator only)