>Is there another national US online bookseller?

Barnes and Noble. Their Nook isn't as good, but it's an alternative. I also will buy books [1] direct from publishers, and there are still more narrowly focused sites like History Book Club and Christian Book Distributers.

[1] I dislike using qualifiers (physical books, postal mail) which turn centuries-old words into phrases. If I mean e, I say/write e, otherwise I mean what the words always meant.