As an emergency services dispatcher, scanner buff, and railfan I hope I can help.
There are many brands of scanners on the market, but the 2 major brands are Uniden/Bearcat and Radio Shack. Uniden/Bearcat and Radio Shack are the easiest to find in most areas. Since you plan to use the radio while railfanning I suggest getting a handheld model. All scanners made today cover the railroad radio band (160-162 MHz). You will also find that most radios come with features that, initially anyway, you may not need, use, or understand. If you live in an area with a lot of local rail activity you may also want to consider a base model scanner for your home and/or a mobile unit for your car (providing scanner use in vehicles is legal in your state).
In regard to railroad frequencies, Kalmback Publishing publishes a softcover book 'Railroad Frequencies'. I don't see it listed on the Kalmbach website anymore, but it still may be available in hobby shops. If you can't find it, there are numerous websites where you can find railroad frequencies as well as at your local Radio Shack store.
In regard to scanner accessories, there is a lot out there. Some of it is useful, some not.
Try these links and happy listening!