I've started to monitor my mood each day using the basic (and free!) version of an online tool called Moodscope. The rationale behind it is that monitoring something health related can lead to positive change. What's more the system can be used to share that information with a friend so you can receive a bit more support at the low times.
What I'm doing is annotating each day's score on the graph to reflect on why its high or low. I've noticed, for example, that keeping on top of things such as housework and record keeping is really beneficial whereas a bad night's sleep really knocks things right off course. This increased awareness gives me an indication right at the start of the day about whether I need to give myself a little extra TLC or make that extra to do something positive and life affirming that helps me get things back on course.