The VMT is a must: http://www.vmt.org/collection.html. Catch the Berk before it heads for Ohio! 1218 is there, next to the 611, under the canopy.
A short walk away is the Link Museum, well worth your time. In fact, you can buy a combined ticket that will get you into both at a discount.
There is a walkway between the two that has a number of railroad displays, many of which actually work (horn, bell, crossing gate) when you push the button…
The covered walkway that you can take over to the Link Museum (in the old N&W station) goes right over the NS main. Plenty of traffic to observe while you’re in the area. And if you want to brave the highway bridge, you can get a view of the NS shops.
All of this is right next to downtown Roanoke, if you’re inclined to wander down that way for a cool one or a bite to eat.
I was there for one afternoon during a business trip to Lynchburg (about 45 minutes away). An afternoon well spent.
Plus, its an old railroad hotel, owned by the Norfolk & Western until they donated it to Virginia Tech who renovated it. Also, right near the Hotel Roanoke are the former Norfolk & Western headquarter buildings which are pretty neat as well (one is now being used as a higher education center).
Lots of fairly accessible railroad history around there - there are more shops and yards visible north of the VMT (take the bridge next to the VMT and take the first left (I think). Pretty much anywhere you get there is something railroad related to see. Even if you go up by the star on Mill Mountain, you can see the trains going through Roanoke.
There is actually a lot to do in Roanoke. One thing that it is pretty famous for is the star up on the mountain and it is also free. There is a zoo that is relatively inexpensive.They also have a transportation muesum. I like the farmers market . One must see is the Roanoke hot dog weenie stand. They make some of the best made to order hot dogs in the area. Do a google search on Roanoke and they actually have a web page with all the events listed. Have a safe trip.