If you’re considering a trip abroad, the Student Universe site is a great place to start.  Don’t be afraid to explore every corner of this site.  You can never have “enough” information!

In preparing for my own European adventures, I’ve collected some additional sites that may be of use to you:

Flights (for those who may not qualify for student discounts)
Inside Trip - Compares flights not just on price but on reliability, comfort, speed, and other factors.
Sidestep: - Good flight search engine.
Farecast: Microsoft’s answer to Sidestep.
TSA Prohibited Items List - Stay out of trouble.
How to Survive Long Flights - Advice from a guy who flies regularly between Australia and Los Angeles. His packing tips saved my last trip.

Helpful Forums
Student Universe Europe Forum - HQ for traveling young people.
Rick Steves’ Travelers Helpline - These friendly folks are good problem-solvers.
TripAdvisor Europe Forums - Good place for finding reviews, local recommendations.
GuideforEurope Message Boards - Will review and critique your itinerary at all stages.

Rail
Train Travel Information - read this to orient yourself with European trains.
How Railpasses Work - Railpass 101 from the site’s namesake.
Die Bahn - European train timetables
Eurail Map PDF - Enlarge to 125% to see detail.
Eurostar - Train between London and Brussels/Calais/Paris

Packing
Packing Light - Too much is just as bad as not enough.
General Packing List. - Ladies should also review the Packing Tips for women.

A little investigation goes a long way.  Remember: well-researched trips = fun times.