4x4 Trails.net
I have found some great trails through this website. Otherwise, I tag along with friends, and see where they go.
I would definitely suggest buying one of those state topo/road maps for your state. When I get bored, I just have a couple friends come with me, and find some strange tiny road I've never been on before, and go till it becomes too technical, or private property/no trespassing signs start showing up.