I still see quite a few CSX 2 bay covered hoppers that still wear B&O and C&O paint schemes, the gray scheme from after the C&O/B&O merger but prior to Chessie, on a fairly regular basis. Also there are still an awful lot of Chessie and Family Lines/Seaboard cars on the CSX roster. NS and CSX also still have a handful of old Erie Lackawanna 70 ton three bay hoppers that they use for ballast and tie service, a good many of which still have their EL reporting marks. Also as mentioned above Penn Central cars aren't too hard too find, especially gondolas, there are even some Pennsy 65 footers roaming around. Then again this is just stuff that I see in the east, out west its probably a whole different story. Also as Otto mentioned a lot of the cars from the "good ol days" are at an age where they are no longer allowed for interchange service, and once a car reached that point it usually doesn't provide much incentive to keep it around.
Scooter