I rarely shop online so my books have mostly been purchased from these shops in Singapore:
Kinokuniya (English, Japanese and Chinese books) — my favourite bookstore (^_^).
Borders (English only) — always get sucked into buying cookbooks when they have their 30% off sale!
Page One (has English cookbooks, but strength lies in Taiwanese publications).
Popular Bookstore (Singapore & Malaysian Chinese/bilingual language cookbooks).
Commercial Press (Singapore, Malaysian and Hong Kong Chinese language cookbooks).
Select Books (English language) — has an excellent collection of books on Southeast Asia and does international mail order.
Carrefour — the cheapest place to buy local cookbooks bilingual Chinese-English cookbooks! But limited range.
Union Book Co. — Chinese bookshop stocking mostly Taiwanese books, with good selection of cookbooks in Chinese from different regions.
Click on the links below for the book lists:
Books in English