As you prepare to feast, it's not too soon to consider the impact of all that turkey and stuffing. The free Lose It! [iTunes Link] has been out for a long while now, and it's an app that people nearly always bring up when the conversation turns to good exercise/calorie tracker apps. With good reason: at one point I managed to lose over 15 pounds, and it was at least partly thanks to Lose It! on the iPhone. Its extremely intuitive interface and vast database of foods and exercises made it incredibly easy for me to track my progress and restrict my caloric intake.
The one thing I always thought was missing from Lose It! was the ability to sync information back to the Mac. The app itself had limited ability to track trends over time, so I always wished Lose It! had some way of getting that info off my iPhone and onto my computer so I could at least make a spreadsheet out of it.
Lose It! has gone one step farther than that -- they've created their own website, loseit.com, that allows you to view all sorts of information, synced directly from the 2.0 version of Lose It! on the iPhone. Not only are there heaps of information about your own weight loss, calorie consumption, and exercise trends, Lose It's website also allows you to view your friends' information and watch each others' progress, assuming you all have the Lose It! app.