accesstoinsight.com. The Buddha’s original teachings in the suttas are here, plus commentaries and articles by Pali scholars.
suttacentral.net. The early suttas translated from Pali into English, plus the Agama’s translated from Chinese. The parallels between these are very important to corroborating what the Buddha taught. Bhante Sujato (Australia) and Venerable Analayo (Germany) were instrumental in this endeavor, and in developing the website, as was Rod Bucknell (Australia) plus many more.
amaravati.org. Theravadan books, video and audio talks. Books cannot be mailed to US, but PDFs are available.
dhammatalks.org. Ajahn Geoff’s website. Translations of the Pali canon, talks, and more.
forestdamma.org Books with teachings by Ajahn Mun and Boowa plus a few more. Hard copies postage-free, plus PDFs online.
Ajahn Geoff (Thanisarro)