Web/iPhone: How happy are you? MoodPanda is an interactive mood diary/journal that measures and keeps track of your happiness, creating neat pie charts and graphs to show you how you've been feeling over time.
Keeping a log of how you feel has been shown to be therapeutic for people who suffer from depression, but it's also useful for others to keep track of things that make them happy. For example, using MoodPanda you can quickly jot down that you were very happy (9) on Monday, noting the sun was out, you exercised and started a new project. You can look back months later and see your progress.
The app lets you update your mood on Twitter and Facebook if you wish as well as send others virtual hugs (on my first day of trying the service, registering an unhappy 3, I got two hugs from strangers almost immediately, which was uplifting, actually).
If you could use a little more happiness in your life or are just like collecting data, give the free service a whirl.