Other than around town, I have found that the best place to freeride is parks. The one I mountainboard at has dozens of trails that wind and bend to really give you a rollercoaster type feel when you ride them. With humps and drop offs included, I don't see how it could get much better as every trail has it's own unique feel. During the fall I hit the rougher steeper trails and literally float over the leaves giving it a real snow like feel. There's even a huge paved road perfect for carving down or bombing down if you want a smooth but fast ride. I haven't found too many other places that I enjoy as much.
The park is basically empty, so when I take a load of people up there we have unlimited possibilites, from using picnic tables for tricks to riding around the camping area and bombing off the ledges near the lake. In fact, we go there so much that the park rangers recognize our cars and often stop to chat with us. It's funny too though, I actually left a mountainboard there and went back to get it and the rangers had a slew of stories to tell about how they each tried it and had a good time cracking up at each other as they bit it hardcore.
Just wondering, but where does everyone else freeride?