I hate to admit it but Rail Europe is quite convenient for making reservations only for those who already have a rail pass. But their reservations are way overpriced and cannot be changed once paid for.
Is there another way to make reservations online? I know you can always make them at the train station, but lines can be quite big at times and the online convenience would be great, if possible. I know DB offers online reservations but only for travel within Germany. None of the other railroads do, to my knowledge.
Most countries' systems do, at least for long-distance trains (certainly SNCF in France and Trenitalia in Italy do, allowing you to print your ticket at home).
Many international trains (Thalys, Lyria, etc) are run as separate businesses and you can book tickets directly on their websites rather than on the national operators'.
Local trains are often not worth booking in advance as in most cases there are no discounts for booking in advance and no reservations.
I always use bahn.de to check timetables anywhere in Europe, and then book the tickets through the local operator's site.