http://www.rrpicturearchives.net/default.aspx
if you like that one, here is another that specializes in older photos:
http://www.rr-fallenflags.org/
Wow...these websites are fantastic! Thank you for passing them on.
Regards,
Ray
May as well throw in a couple of others:
http://www.railpictures.net/
http://www.northeast.railfan.net/