I've tried to keep away from applications that require subscribing to a service, but there are times when it's unavoidable. GeeTasks, Dropbox, and Evernote all have components in the cloud, and keeping up with your travel details is, I think, also a good fit for the cloud.
I've found TripIt to be a useful service for keeping up with my travel, as well as the travel of my colleagues and business associates, so I was pleased to find the TripIt iPhone app.
When it comes to keeping up with my flight numbers and times, hotel and rental car reservations, and the like, TripIt on the iPhone is quite sufficient. And because it takes its info from the data I enter on the TripIt Web site, no additional effort is required.
That said, I'm hopeful that future versions of the software will have more functionality. Right now, for instance, TripIt for iPhone only keeps track of my travel - it doesn't include the "keeping up with my colleagues" information at all. It needs that.
It also offers to send me push updates if schedules or travel details change, but only if I upgrade to the premium edition of the software (how much?).
TripIt does something I need, and it gets the basics right, but its inclusion on this list is based, at least a bit, on the hope that it will come closer to the full functionality of the service in future versions.