One of the oldest and best on the web, the fruit of the work of Karl Keating, James Akin, and Rosalind Moss. The name says it all. These guys are in the business to give you answers. Be sure to read their Starting Out as an Apologist. Also, check out the tracts and other resources available in the: - Library of Catholic Answers
Joe Gallegos' excellent collection of the teachings of the Church Fathers. Organized by topic. Essential for beginning to think with "the mind of the Church."
A great site by a self-described "Catholic Apologist and Free-Lance Writer, Joyful Husband, Daddy, & Celtic-American, Nature-, History- and Music-Lover." Scroll down to "48 Topical Index Pages." Be prepared to spend some time browsing.
An excellent collection of articles and essays on apologetic themes, by the creator of the website: - Defenders of the Catholic Faith
By James Akin of Catholic Answers. A fine collection of links and original materials.