There are three books that I found quite useful.
- McKeachie's Teaching Tips - this is small but dense, packed with good ideas (good to re-read from time to time) - http://www.amazon.com/McKeachies-Teaching-Tips-Strategies-University/dp/0495809292
- The Joy of Teaching by Peter Filene - good for new teachers - http://www.amazon.com/Joy-Teaching-Practical-College-Instructors/dp/0807856037
- Teaching Unprepared Students by Kathleen F. Gabriel - good if you have students who are not really strong academically and you want to help them - http://www.amazon.com/Teaching-Unprepared-Students-Strategies-Promoting/dp/1579222307