Responsa (She'elot u-teshuvot)Rishonim (coming from the root "rishon" meaning first or elders) is a term for the leading Rabbis who lived approximately during the 11th to 15th centuries, in the era before the writing of the Shulhan Arukh and following the Geonim.  The name "Rishonim" is a designation found in the Talmud and applied to authorities who (appropriately) lived before the one who quotes them.  The title is generally used to mean "predecessor" or "ancestor" and to imbue a sense of authority to the text.  Among the most famous of the Rishonim are Rashi, Maimonides, and Nachmanides.

For more on the contributions of the Rishonim, see Responsa (She'elot u-teshuvot), Novallae, and Talmudic commentaries.

Lists of names and biographies

Rishonim, 4800–5160 (1040–1400)

Gives a list with a biography of many of the rishonim.

http://www.chabad.org/library/article_cdo/aid/115536/jewish/The-Rishonim.htm

Rishonim at Wikipedia

Gives an overview of the Rishonim and a list with links to biographies.

http://www.answers.com/main/ntquery?s=rishonim&gwp=13

Finding texts online

Seforim online

http://seforimonline.org/

This site focuses on the works of the Rishonim and Acharonim and includes some of the Geonim.

Responsa Project - Torah literature and Jewish texts | פרויקט השו"ת - ספרות תורנית

This database includes Torah, Talmud, codes, and commentaries in addition to works of responsa. Texts are available in Hebrew only. Basic searching is available to anyone, but advanced features are only available to subscribers. Members of the HUC community can access more features through the Jewish Studies Portal.

Maimonides at Treasures of the JNUL

Includes digitized images of his manuscripts and early print editions.

Maimonides' Mishneh Torah

http://www.chabad.org/library/article_cdo/aid/5634/jewish/Mishneh-Torah-Hebrew.htm

In Hebrew.