I buy a lot of books at Diesel. I get discounts from handing in a bunch of $.50 reviews. And there is no tax for the books that can be sold in Canada. Worst search engine in the world though. It's hard to find the books you want at times. The customer service isn't the best either. But with points I get near half off each book I buy there.
I do consider Kobo more helpful though. And Sony never has preorders.