Most of the various European rail passes available are for specified countries. Do they apply for travel into or out of that country, or are they valid only for travel entirely within that country?
In other words, if I had a railpass for Germany, would it cover a fare from Amsterdam to Cologne, or from Dresden to Prague?
As far as I know, they are not good for travel outside the specified area. When I went to Europe, I had a Eurail pass that took me from Helsinki to Paris. My next destination was London, which the pass did not cover. However, it offered a 50% discount on the Channel Tunnel train. I still bought that ticket separately.
There are many different kinds of Europe rail passes, many of which do allow travel within throughout EU. I imagine many of them don’t cover the UK though.
There are various online companies that sell them and it would be worth shopping around for the best deals based on which countries you want to visit. A Eurorail global pass, for example, would allow you to travel between 21 different countries. The Netherlands, Germany and the Czech Republic are included. Info on that, here. Might be cheaper for going something with more specific countries though.
There’s the eurail passes, which work pretty much everywhere except the UK.
Depending on how much you’re going to travel between countries, it might be cheaper to get single tickets, though.
Also keep in mind that national railroads may have specific “special deals” that allow for cheap travel within that country, depending on the date you’re there. For instance, the Dutch NS currently sells “lentetoer” tickets that allow 2 people to travel 1st class throughout the country for € 39,50 (€ 19,75 per person per day). They also sell 1-year off-peak discount passes for €55 (40% reduction on all normal tickets after 9 am), which you can use with up to 3 other people.