The coolest mental exercise I have found so far is called stumbleupon.com.

You chose a category of interest, and it feeds you website after website. If you like one of the sites they showed you, you click “I like it.” After a while, they have a pretty good idea of what turns you on, and they just keep feeding you material that you’ll love. For example, when I am feeling burned out, I choose the category “Photography,” and they show me wonderful things. It is completely free. I guess I just crave input.