Authorized (they pay me royalties) electronic copies of my books (including Tor titles) are available at Baen Ebooks (http://www.BaenEbooks.com).  Baen’s Bar has two discussion areas where you can get more information about e-book formats for various readers:  Webscriptions EBooks and EBook Reader.

My available e-book titles are listed at http://www.baenebooks.com/s-32-david-drake.aspx.  Instructions for downloading for the Kindle, the Nook, and other devices are at http://www.baenebooks.com/t-ereaderinstructions.aspx.