I haven't tried this yet, but Ann Oliveri sounds enthusiastic about TripIt, an online travel organizer. in this post, Ann says,
To create a trip, you just forward purchase confirmation emails to TripIt to create a master itinerary for air, hotel, and more. You can add details as you confirm them, and not worry about juggling a dozen emails, frequent flyer numbers, hotel addresses, log ons, or contacts. Best of all, you can access all the details in one place anywhere—and easily share itineraries and travel calendars with friends, clients, or bosses.
It sounds like a good deal, particularly since it's free.