If you visit Japan there is a good chance that you will be taking the Shinkansen.

Be sure to stop by the Japan Railways Site and check out Hyperdia.

Hyperdia is a search engine that allows you to enter the start point and your destinations site and get the trains, times, and cost to get to your destination.  The Nozomi has all reserve seats, but the Hikari and the Kodama do have both reserved and open seating.

Hyperdia is an invaluable tool for planning your trip or trying to find the best train to catch to make it to your destination on time.