The exam wasn't very difficult; 35 multiple choice questions. It probably took me less than 10 minutes to finish the test. I used three things for studying:
1. "Now You're Talking!" published by the American Radio Relay League.
2. "Amateur Radio No-Code Technician License Examination Study Guide and Workbook," by Bruce Spratling, W8BBS. (PDF document.)
3. The free online tests at QRZ.com.
If you're interested in taking the Tech exam, my suggestion is to read through Now You're Talking!, and review all the questions at the end of each section. Then go through the PDF. Finally, take as many of the QRZ.com tests as you have time for.
I've found some good websites about ham radio, too: