transcendental meditation
Robert Forman has done TM for many, many years, and he writes about his experience in this book:
http://www.amazon.com/Enlightenment-Aint-What-Its-Cracked/dp/1846946743/
His perspective is balanced and thoughtful.
You might also be interested in my meditation blog which is often (particularly in earlier posts) but not always from a rationalist perspective:
http://meditationstuff.wordpress.com/2013/12/22/experiences-of-long-term-meditators/
Motivating, appreciated.