This site has science activities that are broken down by grade level and topic. The activities are informative and would be fun for the kids to try after learning about a topic in science.
EducationCity is a subscription website that features games for grades K-6 in math, language arts, and science. With the subscription, students can keep track of their progress in the games with the "success tracker", and then the teacher gets a compilation of student scores, broken down by subject and graphed to show how they are doing. It can be used individually with students, or in the "Interactive Whiteboard Mode" whole class/small group.