Thanks everyone! This is all good input. I actually live only a short distance from the VA Creeper Trail, so I highly recommend it to those who haven't ridden it. I do recommend keeping the Damascus to Whitetop section (if you're pedaling up instead of down) to weekdays. Weekends get super crowded with kids flying off the mountain on bikes they aren't used to handling.
I am familiar with the New River Trail, but haven't been there yet. Also, those of you who mentioned the C&O....I have researched it and gotten very mixed reviews. Would a gravel bike be best? Or mountain bike? We ran into a group of guys on the GAP who had ridden the C&O, and they did not have good things to say about the trail and gravel bikes. I would really like to continue that ride from Cumberland on to DC if the trail is good!
I am also excited to check out the Pine Creek Trail that was mentioned. Thanks for the suggestions! Keep them coming! I am also a Rail Trail conservancy member and supporter, but I have traveled to some trails that have been super grown up and had zero supporting infrastructure (you know....like cold beer after a days ride), so I like to get the low down from fellow riders as well.