Introductory Books
For English language speakers, a great place to start is with a hardcopy of Bhikkhu Bodhi’s book, In the Buddha’s Words. Check out the Dhamma Wheel discussion forum’s post In the Buddha’s Words — Open Source Version and the corresponding information here. For a very modest price, you can even listen to In the Buddha’s Words read by Fajer Al-Kaisi via two MP3 format CDs. Caveat: although the recording quality is excellent, the pronunciation of the Pāḷi words is sadly naïve. (For example, the “Th” in Theravāda is pronounced like the ‘th’ in ‘the’.) For a more detailed consideration of the book, you may listen to the 45-lecture series, A Study of: In the Buddha’s Words, given by Bhikkhu Bodhi from September 2007 to October 2009 at Chuang Yen Monastery in Carmel, New York.
Another (quite early) overview, Nyanatiloka’s The Word of the Buddha (first published in German in 1906) is still available online (14th edition, 1967). Walpola Rahula‘s What the Buddha Taught is also a very good, though brief, introduction.