Go Europe
  From About.com Guide Durant Imboden, who offers three pages of excellent links to a variety of helpful sources.

Go Eastern Europe
  Scroll down to the "train travel" section by About.com Guide Bill Biega.

Europe: BritRail
Here's the gateway to Britain and Ireland's excellent rail system. Remember: In these places, you need Britrail passes, not Eurailpasses.

Europe: Deutsche Bahn
German National Railway's excellent web site offers train schedules in English for virtually every train station in Europe. Travel times, costs, routes of travel all right here.

Europe: Eurail
The Eurail system can be a big money saver. This site includes tables for finding the cheapest pass that meets your itinerary's requirements.

Europe: EuroNight Service
You can save a lot of money sleeping on trains. Swiss National Railroad maintains this site, which shows a variety of comfort levels and prices for overnight travel.

Europe: European Railway Server
This site will link you with every major government railway system in Europe. Handy if you want to focus on a single nation.