we ride Wonder lake daily. It is pretty big, and usually traffic free. The downside is the depth. It is pretty shallow, so we have to load up the boat pretty heavy.
The fox is cool during the week, but also pretty shallow.
The Chain is huge, some deep lakes, some shallow lakes. The only problem is that it is completely unrideable on the weekends due to traffic.
If you feel like driving a bit, The Illinois river down by Ottowa is really nice. mostly natural shorelines, deep enough for commercial traffic, and you can always find a good run.