If you haven't visited MemoWare, you should...it's perhaps one of the larger eBook/eDoc sites out there, and supports a bunch of formats. Has some pure books, some guides, lists, etc...an eclectic mixture, but interesting.

MemoWare Web Site (http://www.memoware.com/)

Slick Trick: Become a member and you can specify the formats you're interested in and receive e-mail updates when new titles are posted in your formats.