The best trails are near Williamsburg. Check out these:
York River State Park. Recently expanded 12miles of MTB trails. Great singletrack and fire roads
Freedom Park. Approx 19miles total. The C loop is a favorite with lots of TTFs.
New Quarter Park
Check out the EVMA website. It has a listing of all the trails they maintain (which are pretty much all in Williamsburg). Some great trails in the burg and it's not too far away. There is also a trail network in Newport News near the Riverside hospital that is "unofficial" and there is Ipswitch in Chesepeake that is fun at night.
EVMA is where its at and also you can catch up with Southside EVMA's facebook page for some more localized updates and organized rides over your way. I'm in Virginia Beach and we tend to ride Ipswhich during the week and head to williamsburg on the weekends.