I would say Andrew Wright's 1000+ Pictures for Teachers to Copy is the best, most useful book I've read in 25 years in English teaching.
It's practical, it's useful, it will save you (and your learners) lots of time, it's fun — and it teaches you a skill that I think all teachers should have, especially anyone teaching young learners.
You can't draw? You don't need to be able to draw — all you've got to do is learn how to copy a few simple images.
Publisher: Longman ELT, ISBN 0175571007. Available from Amazon.com.