Have you heard of Mood Hacker? It's a free online tool that tracks your moods by mapping it against your thoughts, feelings and actions over a period of time. After awhile, you'll start to see patterns. They say if you keep doing what you do on good days, you'll be able to affect your mood for the better.
Think of it like Mint.com for the mind. Try it. It's quite fun. I'm looking forward to seeing what my chart looks like a month from now. Bad moods, be gone!