This is an example of using Powerpoint to create a game of Jeopardy with your students. It creates an element of interaction that otherwise wouldn't be possible with the computer.
This site has an activity which tests the students' knowledge of the different states in the United States. Students click and drag each state to its correct place on the map. Great for students who are learning about states and capitals.
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.
This site had online talking story books that could be used on an interactive whiteboard. This could be done as a whole class or used in small groups of students.
This is a page on the scholastic website that has interactive whiteboard activities for Earth Day. These activities include lessons on water conservation and recycling etc.