No need to say that the options are much more expansive now!
The real problem now is picking out the books! To help pick what to buy, one of the easiest ways is to look up the title (in quotation marks: that will make sure that all the words are kept together and give you a better chance of actually getting that book near the top of the list!), or type "ISBN" followed by the number of the book into a search engine. This will give you (hopefully!) a few reviews and maybe even a less expensive store to purchase from. Be very sure to check out the store that is offering the book, though.
My favorite source of books is Amazon.com. Not only can you read industry and customer reviews, and find great prices with excellent service, but you can also sell your used copies of books that you don't need. Most of the books that we use for school have been bought used from Amazon.com at less than half the cost of new. They also have excellent policies that protect buyers and sellers of used books, and offer free shipping on new items when the order is over $25. I've been buying from them frequently since 1999, and I've never gotten the wrong order from Amazon. I've been buying used books from them since 2001, and the few issues we've had with used items have been satisfactorily resolved with ease. I've never been ripped off!
Half.com has a fair selection of textbooks and children's books. I often compare prices between Amazon and Half.
Ebay is another good source, even tough they now refuse to carry teacher's editions. The auction format can be a bit difficult if you are in hurry.
There are several smaller sites that cater to home school curriculum needs. A few that offer new and used are :
VegSource Talk and Swap Homeschool Boards
A wide variety of curriculum available, divided into grade levels. No particular safeguards are in place, so buyer beware! All in all, though, it is a very good place to find certain types of curriculum.
A consortium of used booksellers with over 60 million books available at generally good prices.
New and used books. 30 day money-back guarantee, not an auction or third-party seller site.
A wide-ranging site with book sales and trades, and other news.
The Book Cover
New and used books, not an auction or third-party seller site.
A general used book store with some textbooks. The prices are often excellent!
The Homeschool Mom
A Yahoo! Board for buying and selling curriculum.
Campus Books 4 Less
This site checks several of the top college bookstores for the lowest prices. Great for high school kids!
Aussie Homeschool Classifieds
A community online.
For suggestions about which books to buy, try:
Homeschool Store (Canadian version)
Homeschool Store (US version)
Homeschool Store (UK version)