I've ridden from Staunton to Lexington a couple of times. You can stay on 252 to 39. Nice roads all the way. You can also take the backroads route that the Tour de Valley takes as neal mentions. That follows Glebe School, Summerdean, Walker Creek also down to 39.
Here's a route I did last fall that goes from Waynesboro, Staunton, Lexington, Buena Vista, and back on the Parkway:
http://connect.garmin.com/activity/123558822