Overseas Online Bookshops
I have personally bought books from at least eight
overseas online bookshops. These days I mostly use
Book Depository,
Amazon or Amazon UK (there
isn't yet an Amazon Australia).
International postage charges can be quite steep so for many books local bookshops may be cheaper. However some overseas bookshops now offer free international postage.
Prices can vary considerably between shops. The price comparison sites I use most are AddAll, Bookfinder, and Booko.