When I was in Portland I visited Powell's bookstore, the hugest bookstore I have ever been to. It was not too busy, so it didn't really feel overwhelming. I'm an avid science fiction fan, and they had
half a room of science fiction/fantasy books!! The most I've ever seen in one place, I think! And the best part was that they had a lot of used books, so I bought my paperbacks for about $3.50 each, as opposed to seven or eight dollars I usually pay for a new book.
The selection was amazing. While many stores have a single section of religion books, Powell's had separate rows for Christianity, Judaism, Eastern Religions, Astrology, and others.
And there was a coffee shop too.
So what's the best bookstore you've been to?