kristian - although the Harry Potter series were kinda unique in that they were originally written for the younger crowd - they caught on in the adult world because of the humor that was written at the adult level that the younger crowd didnt understand
the two series I can think of are both available at Amazon:
The Chronicles of Amber (there's 10 of them I believe) that you can get all in one book - by Roger Zelazny - they have a fantasy theme and the magic - although be careful as another author then wrote some other books carrying on after the author died as well as the authors son
The other would be the Xanth series by Piers Anthony - there are about 24 of these - I believe A Spell for Chameleon was the first in the series - a lot of humor and magic and a similar hero or lead character