FitDay: This site helped me work off 10 pounds by forcing me to report honestly the foods I was eating every day and their calorie counts. No more delusional fits of denial ("That donut couldn't have been more that 75 calories!"). FitDay isn't the only site that does this, but the breadth and depth of its food information and its easy-to-use layout lift it above the rest.
RealAge: Fill out a health questionnaire at this site, and it will report your "physical age" (the age of your body), which you can then compare with your chronological age. If you're in good shape, your body may be 35, even though your calendar age is 45. Or vice versa, if you aren't fit. Either way, the site produces a detailed health plan to lower your physical age.
SparkPeople: SparkPeople offers a smorgasbord of nutrition, health, and fitness tools, plus support from experts and a large social network to supply empathy, new fitness ideas, or advice. The site also provides interactive tools such as fitness trackers and detailed meal plans (also free). Finally the site has a great app for the iPhone, so you can check in with the site while you're at the grocery story or the gym.
I hope that at least one of these tech products proves intriguing enough for you to try. Sometimes all it takes is one thing--in this case a faithful tech ally--to help you make the right choice between staying rooted to the couch and getting up and getting your game on. Oh, and please chime in at the PC World Forums to let us know which gadgets, sites, or services have helped you maintain your svelte figure.
Good luck and good health in the year to come.