Local library is a huge one for me. Sometimes I just go browsing, other times I look up authors or books I've heard about and look for similar books by the same or other authors online. Sometimes I browse around Chapters to see if anything's interesting. I'm fairly plugged in, so I sometimes get book recommendations from blogs, sites, podcasts, vidcasts and so on. Sometimes I get recommendations from books, or by reading the bibliography at the end of books.
At amazon, once you've found something you find interesting, look around its page because it usually has a listing for "similar" stuff.
I read books on a variety of subjects. I've just recently started reading "PD" books like from Tony Robbins and Brian Tracy and so on. I rarely read any fiction, mostly non-fiction. I'm learning to photoread so I'm starting to get through the stuff faster, too.
There's been a coupla threads online here about people recommending books, some really good ones there. Here also:
http://www.stevepavlina.com/personal...ment-books.htm
HTH.