It doesn’t matter if you’re a frequent flyer or just catch a flight now and then. As long as you like to keep track of where you’ve been and how you got there, Flightdiary is worth checking out. Flightdiary lets you keep track of just those things for free.
You’ll get a personal profile with a map and, depending on what details you add (airline, aircraft, date, time, etc.—it’s up to you), detailed statistics about your flights with graphs on CO2 emissions, top airports and airlines, etc. Your profile can either be easily linked to the Flightdiary community, or set as private; again, it’s your choice. The only negative is that there are lots of ads—but what else would you expect from something that’s free?