If you're looking for royalty free graphics that are outside the realm of Microsoft Word, check out Clker.com! I've found a bunch of useful art on here to illustrate rubrics and other school projects.
246 Christian images available for use
Terms - This gallery contains many original and unique images that can be freely used for personal, evangelistic, church and other non-commercial uses. You will find herein a blend of digital painting, 3D graphics, and digital photography. It attempts to remind visitors who God really is, what he has done for us, and to encourage and reassure Christians in their faith.
Laura Schwertfeger shared - lots of nice Christian photos, videos, etc. There are many available for free, others for purchase. Even the ones you have to buy do seem much more affordable than some of the istockphotos I have looked at lately.
Gorgeous graphical periodic table elements resource - have to see to believe. Great classroom resources when studying the periodic table or even simpler with little grades - just showing what they look like in three D movement.
An interesting site which discusses illustrating the Bible along with providing links to sites which may provide some good Biblical graphics which might, depending on the copyright permissions of course, be useful for pastors, teachers, churches and church schools. (Check out the 2008 interview with one of my favorite modern Bible illustrators, Annie Vallotton.)
Called a "personal internet desktop", Symbaloo is a way to graphically show your bookmarks. Del.icio.us bookmarks can be linked with this service - I see a lot of good uses, especially for lower grades if this were set as the home page of an Internet browser.