I've used TripIt. Reading your email is central to their "magic." The idea is that whenever you get any sort of travel confirmation, they automatically ingest it and compile all the info into trips, then handle stuff like reminding you to checkin, auto-filling up your checkin code, suggesting seats, etc.

They also have an alternative for the privacy-minded where you just forward any confirmation emails you want them to know about and the same stuff happens, but for the email address I was using for this, there wasn't anything I was worried about them accessing, and this was easier.