This has always been one of my frustrations when I go home to visit my family. I usually run on the Wiowash (sp?) trail, but find it to be pretty boring (flat, out and back, straight). I have gone to High Cliff and found those to be O.K. What is Hartman Creek like? I might have to go out there sometime.
I know it is far away, but probably my favorite run in the world is Indian Lake outside of Madison. It may be more for sentimental reasons than anything else (it was were I ran all of the time in college), but it is also a great set of loops through the woods- good hills on it too. It is far from Oshkosh, but I thought I would just throw that one in there.
Sorry that I can't help more.