Great thread! I too am a believer in a daily gratitude list ... it seems to start my day off in the right direction. I find that it rewires my brain ... after more than a year of starting most mornings by writing down 5 - 10 things I am grateful for, now I find that the habit of turning toward the positive is much stronger.
I'm often just writing "small" things on my morning list -- I'm grateful that a hummingbird just passed through my backyard, I'm grateful that it's cloudy today because it will make it cooler when I exercise. But weirdly, that has re-wired my brain so that when "big" things happen, I respond by seeing the positive more than the negative.
Meditation and mindfulness also help me become aware of when negative thoughts are arising, and give me a choice ... I don't have to follow those thoughts or entertain them, I can just see them and let them go.
Of course it's all a work in process ... takes daily attention and I still entertain negative thoughts some times. But the trend is toward the positive, as long as I put in a little bit of effort every day.