I use Yahoo email and there is a nice Calendar feature. Every day I add a new event and entitle it "Mood Diary - Angry" (or whatever the main emotion was for that day). Then at a glance I can look at it and try to determine a pattern. It's quick and easy and I can make a few notes in there about why I felt that way (fought with mom, bad day at work, etc). I've only been doing it for a few weeks so I haven't seen a pattern yet... but I've been doing it pretty diligently. I'm in front of a computer for 12+ hours a day so it's pretty convenient for me. I suppose you could really use any calendar type program for this!