As someone who has come up with some of her best ideas while washing dishes, I found this post by Katie Konrath to be very interesting. She points to survey results from Idea Champions that list daydreaming, showering, gardening, and driving as some of the best ways to take a break and allow the mind to get creative.
It bears out what I've discovered about myself, and even about the kids that I've had on different teams. When the ideas just won't come, it's better to take a break from focusing on the problem than to continue forcing it.
Sometimes I think of the inside of my head as a rock tumbler, where the ideas need a chance to bounce around against each other before they come out looking like they have some potential. Where do YOU come up with your best ideas?