Happiness Jar
This is a very neat idea of Elizabeth Gilbert: a Happiness Jar:"Every day (well, almost every day) I write down the happiest moment of that day on a small piece of paper, and I fold it up and put it in this big jar. Then later (days, months or years later) when I am feeling blue, I sometimes reach into the jar and pull out a memory (one that would otherwise have been long forgotten) and I can remember one of the simplest and best random moments of my life."
What a great idea - it is something I have to start doing as well - but then again: I never feel blue!