Eyes on the Solar System
NASA just released this extremely cool tool for exploring our solar system. There are some very simple features: changing the date and time, speeding up and slowing down time and jumping from satellite to planet to comet. There are also some very complex tools: size comparison, measurement and ride along features just to name a few.
You do need to download plug in to use Eyes on the Solar System so teachers trying to load this on classroom computers may run into some problems but, it is a very safe plug in and, if you can get around the IT blocks and get the plug in downloaded, you'll be in great shape.
In an elementary classroom you could use this in a whole class setting to compare the size of planets, satellites and moons since they have a visual comparison feature. In a middle school setting this could be used in a whole class setting or by individual students to explore different bodies in space as well as use the more advanced, number based measurement system. In a high school setting students could use this individually or in groups to study orbits, compare the sizes of planets and other bodies. At all levels this tool could be used to simply explore the galaxy and give students a different perspective.
The tutorials are a must and it's something the teacher really needs to play with before turning the kids loose on it.