Heavens Above - Website for tracking Satellites, Space ships and other space objects.
Space Engine - Space Engine is a realistic virtual Universe you can explore on your computer.
Celestia - Real-time 3D visualization of space
See A Satellite Tonight - Free web app to explore satellite locations.
Stellarium - Stellarium is a free open source planetarium for your computer.
Orbitron - Orbitron - Satellite Tracking System written by Sebastian Stoff.