Science Classroom Clip Art - a collection of chemistry icons and images. The site is time consuming to navigate since there is not a search bar.  Grade = B-             http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Science/Chemistry

Discovery School - this collection of science clip art is probably suited more for younger students, however some clips are included of scientific instruments. The site is convenient in that all 52 science clips can be viewed on one page before selecting.    Grade = A-                http://school.discovery.com/clipart/category/scie0.html

#1 Clip Art - collection of clips conveniently divided into categories and sub categories. Pop up ads do slow down your progress a little bit.    http://www.1clipart.com/1clipart.cfm?p=Science        Grade = C+

Molecular Expressions - a collection of images taken from under the microscope. A huge range of images are available, divided into categories.
Grade = B   http://micro.magnet.fsu.edu/micro/gallery.html

Clip Art Gallery - science clip art divided into 3 categories: Plants, Stars and Planets, and Other Sciences. A few of the clips are animated.  Grade = B    http://www.clipartgallery.com/science_nature/science_nature.html

Microsoft Design Gallery Live - site from Microsoft allows you to search for images in collection. Collection also contains animated clips, wallpapers, and backgrounds.     http://dgl.microsoft.com/    Grade = A+