I really like TripIt.com to keeping track of my travel plans. Their iPhone app is alright but it is a read-only view of your plans. Items like the maps require internet access. The folks at Mobiata have taken this a step further. Presently it is still read-only from TripIt but they promise to send updates back in a future version. For now it is sufficient to be able to add notes on you iPhone on the go. The GUI is very pretty. TripDeck offers additional features that require Internet access but give you updated flight status, gate and even baggage claim information on the go.

When I travel I keep my plans in a combination of on my calendar, in my email, and in notepad so I can refer to them while on my trip. TripIt.com is a web site that lets you aggregate your travel plans in one place and download them to your iPhone. They have a unique service that lets you simply email your itinerary to them and they will post it on your Trips list.