One idea that some photographers use to exercise the mind is to publish a Photo-a-Day (PAD) journal. Over the course of one year, internet access willing, the goal is to post one photo that was taken throughout the course of a day, every day, for one year.
Personally, I have two reasons for doing a PAD journal. First, it is a way to document your life through a series of photos. No matter how mundane a photo may appear there is some meaning behind it. The Second reason is to exercise my photographic mind. It will force me into taking a new perspective, literally and figuratively, on the objects that occupy my daily life.