The Sutta Pitaka, the second division of the Tipitaka, consists of more than 10,000 suttas (discourses) delivered by the Buddha and his close disciples during and shortly after the Buddha's forty-five year teaching career, as well as many additional verses by other members of the Sangha. More than nine hundred sutta translations are available on this website.

The suttas are grouped into five nikayas, or collections:

Digha Nikaya
The "Long" Discourses (Pali digha = "long") consists of 34 suttas, including the longest ones in the Canon. The subject matter of these suttas ranges widely, from colorful folkloric accounts of the beings inhabiting the deva worlds (DN 20) to down-to-earth practical meditation instructions (DN 22), and everything in between. Recent scholarship suggests that a distinguishing trait of the Digha Nikaya may be that it was "intended for the purpose of propaganda, to attract converts to the new religion." 1
Majjhima Nikaya
The "Middle-length" Discourses (Pali majjhima = "middle") consists of 152 suttas of varying length. These range from some of the most profound and difficult suttas in the Canon (e.g., MN 1) to engaging stories full of human pathos and drama that illustrate important principles of the law of kamma (e.g., MN 57, MN 86).
Samyutta Nikaya
The "Grouped" Discourses (Pali samyutta = "group" or "collection") consists of 2,889 relatively short suttas grouped together by theme into 56 samyuttas.
Anguttara Nikaya
The "Further-factored" Discourses (Pali anga = "factor" + uttara = "beyond," "further") consists of several thousand short suttas, grouped together into eleven nipatas according to the number of items of Dhamma covered in each sutta. For example, the Eka-nipata ("Book of the Ones") contains suttas about a single item of Dhamma; the Duka-nipata ("Book of the Twos") contains suttas dealing with two items of Dhamma, and so on.
Khuddaka Nikaya
The "Division of Short Books" (Pali khudda = "smaller," "lesser"), consisting of fifteen books (eighteen in the Burmese edition):
  1. Khuddakapatha — The Short Passages
  2. Dhammapada — The Path of Dhamma
  3. Udana — Exclamations
  4. Itivuttaka — The Thus-saids
  5. Sutta Nipata — The Sutta Collection
  6. Vimanavatthu — Stories of the Celestial Mansions
  7. Petavatthu — Stories of the Hungry Ghosts
  8. Theragatha — Verses of the Elder Monks
  9. Therigatha — Verses of the Elder Nuns
  10. Jataka — Birth Stories
  11. Niddesa — Exposition
  12. Patisambhidamagga — Path of Discrimination
  13. Apadana — Stories
  14. Buddhavamsa — History of the Buddhas
  15. Cariyapitaka — Basket of Conduct
  16. Nettippakarana (Burmese Tipitaka only)
  17. Petakopadesa (Burmese Tipitaka only)
  18. Milindapañha — Questions of Milinda (Burmese Tipitaka only)

Notes

1. Bhikkhu Bodhi, Connected Discourses of the Buddha (Somerville, Mass.: Wisdom Publications, 2000), p.31, referring to Joy Manné's "Categories of Sutta in the Pali Nikayas and Their Implications for Our Appreciation of the Buddhist Teaching and Literature," Journal of the Pali Text Society 15 (1990): 29-87.

See also: "Befriending the Suttas: Tips on Reading the Pali Discourses"