In addition to the trails Knappster mentioned, the loop from Animas Forks to Lake City via Engineer & Cinnamon Passes is a easy run. It makes for some spectacular scenery and a good day of trail riding.

I would recommend you buddy up with someone to travel the trails together. You'll find a lot of people run solo by default, but are more than happy to pair up for a run. It's also a good way to make new friends! Although many of these roads are well traveled, it never hurts to have another vehicle in your party just in case.