One of my favorite elementary science sites is sciencenewsforkids.org

This site has short science articles organized by categories like Animals, Earth, Plants, and Weather. There are also resources like the Gamezone, the SciFair Zone, and the Teacher Zone.

Applications for Science Teachers: Science News for Kids is a great source of short expository text to use for teaching/supplementing instruction in a science concept and also teaching a reading comprehension strategy. Quickly print off a short piece of text that students can write on to practice a reading strategy. The Teacher Zone also features an article with supporting questions each week. The site could be a good source of information for student research.

You may want to check out Science News.