Another fascinating set of exercises (that I became aware of reading an article on Ithkuil, an invented language, that was on here a little while ago) is "deconcentration of attention". There's a simple website at http://deconcentration-of-attention.com/, which happens to talk about its applications to software engineering. It's somewhat similar to meditation, and focuses on harnessing the parallelism of the subconscious mind to think more non-linearly.
It seems pretty out-there, and I'm not sure if anybody has really had any success with it, but just reading the exercises is quite intriguing to me (e.g. try to hear "red" in your head, visualize "red" without the word, and then try to feel "red" without visualizing it). Another exercise I thought of after reading the page (and which is quite hard for me, it turns out), is to count in your head without subconsciously speaking/hearing the numbers.