When I fly, I check a few websites to ensure I will have a hassle-free experience. Below are a few you may want review before you reserve your next flight.
Seat Guru will give you information on seat selection so you know if your seat has a misaligned window or extra legroom, etc.
Route Happy aggregates some key factors aggregating data on aircraft type, seat pitch, on-board entertainment, connections, etc to help you select a good flight.
Flight Stats has data including information on the historical on-time performance of your flight.
Flight Radar 24 which shows you all flights in the air around the world. You can click on a plane to see its origin and destination. You can filter by airport to see all flights headed to/from your city. It's a lot of fun to play around with.
Airline Empires is a web game that lets you run your own airline deciding where to open routes, how to price them, what aircraft to purchase, etc. and compete against other real people running their fictional airlines.