Online
LDDEBATE.org: a useful website where debaters (mostly novices) discuss current debate topics and share cases.
Logical Fallacies: Important reading in order to learn the difference between a good argument and a bad argument. After reading this, not only will you learn to make your own arguments stronger, but you will also learn to spot flaws in the arguments made by your opponent
Wikipedia Article on Lincoln-Douglas Debate: This will provide a good overview for the overall structure and terms for Lincoln-Douglas debate.
Wikipedia Article on Public Forum Debate: This is a basic rundown of everything that you and your partner need to know before going into your first Public Forum round.
Books
Lincoln-Douglas Debate: Values in Conflict by Jeffrey Wiese. This is the basic textbook that our team uses as reference for Lincoln-Douglas debate in general. We have classroom copies available for check-out.
Forensics: The Winners Guide to Speech Contests by Brent Oberg. This is a great guide to the individual speech events that our team participates in. If you are interested in IE's, you should try to buy a copy of this book. I got it for a few dollars at Half-Price Books in Crossroads.