For a nuker, the Ivory Tower Pit should be good, as should the area right around IT. Then Outlaw Forest (a little north of Ivory Tower) for 50+. Alligator Island would be good in a group. But for solo, I don't know. The mobs are almost all 2x (or 3X), which is ordinarily not a good situation for soloing nukers.
Also DV is a possibility starting at 45 or a little higher.
When you level at Ivory Tower, don't forget to talk to "Magic Trader Cema" locating at Hardin's Academy for the Quest.
You can get enchant scrolls and Items such as cursed bones.
It's really worth to do.
You could maybe try Pavel Ruins near Schuttgart. I went there on my BD and he leveled very quickly from 48 to 49, but I'm not sure how a Nuker would do there. Because I remember seeing a lot of mobs with the Strong M.Def. thing under their name.