Check Indiebound's extensive listings. Or, if you have a local store but can't find it online, take a few minutes to dust off that phone app and call it, if all else fails.
Indiebound
Indiebound's entire mission is to support small booksellers, and it's been doing so since 2008.
Unlike other sites on this list, Indiebound's web presence is mostly an aggregator.
The site's search engine links to listings on local bookstores' websites, as well as to sites for buying eBooks and audiobooks.
Bookshop
For every purchase made on Bookshop, 10 percent of the sale goes into an earnings pool. That pool is divided among local booksellers every six months.
Shops can also create their own pages on the site, which users can then find via a location-based search. All proceeds from those sales go straight to the respective sellers.
ThriftBooks
ThriftBooks is the place to go for used books. The company buys up excess library books and surplus thrift store stock, sorts them for quality, and lists them for sale on its website.
There's really nothing better when it comes to finding inexpensive books. Many on the site are under five bucks — even with shipping that ends up being less than retail to buy it new.
Better World Books
Every time you purchase a book from Better World Books, the company donates another book to an organization such as Feed the Children or Books for Africa. BWB also funds literacy programs and grants.
BWB helps the environment by ensuring unused books are re-used or recycled. The site even has the option to pay a few cents extra to carbon-balance your order.