I check the top free Kindle books list every day, and they have Master Your DSLR Camera: A Better Way to Learn Digital Photography up today. I haven't read it yet, so I can't say how good it is... but hey, it's free
http://www.amazon.com/Master-Your-DSLR-Camera-ebook/dp/B0094KRID4/ref=zg_bs_digital-text_f_22
http://www.amazon.com/Master-Your-DSLR-Camera-ebook/dp/B0094KRID4/ref=zg_bs_digital-text_f_22