The American Association for the Advancement of Science (AAAS) has an annual award for the best science books.  The 2007 winners are:

Picture Book:

An Egg Is Quiet by Dianna Hutts Aston.

Middle Grades:

Team Moon by Catherine Thimmesh.

Young Adult:

Tigerland and other unintended destinations by Eric Dinerstein.

Hands On Science:

Thomas Edison for Kids by Laurie M. Carlson.