Since I'm participating in PiBoIdMo (30 picture book ideas in 30 days, started by Tara Lazar), I thought I'd pass along this tip.
When I want to find out what other books have been published that relate to one of my ideas, I check out the Children's Picture Book Database at Miami University. This free resource allows you to search by keyword to find books written on your topic. It's also a great resource for teachers looking for picture books to address a particular lesson topic.
Do you know of any good resources for finding out about picture books?