last january i picked up a fitbit from the 1st microsoft store in scottsdale, arizona and any list of apps wouldn't be complete without mentioning this (and it's hardware + device software + web application) since it's something i've used pretty regularly.
1) start with or without the hardware. you can sign up at fitbit.com for a free account
2) with the fitbit device keeps track of the steps you take and also pays attention to whether you are getting a good night's sleep!
3) the device transmits the data to the web service through a base station. i'll post some pictures as follow up.