SeatGuru.com is a simple and clever site that provides seat information for most of the aircraft on almost all the major airlines. Clicking your airline and then the type of plane you'll be on will get you detailed diagrams showing "good" seats and other important information.
Many airlines now allow you to select seats and print boarding passes online, and this is a great way to take care of business before you get to the airports. Preprinted boarding passes often get you to the gate much faster if you have only carry on luggage. When I'm travelling alone I tend to pack light and just lug my luggage around to avoid the hassle and delays of checking my bags. I can then print up my pass and avoid the ticketing lines and head straight for the gate.
With the family this does not seem to be worth the trouble of keeping track of all the bags during flight transfers so we generally print the boarding passes but then check the luggage at the airport.
