A "Where's Spirit Right Now?" page has been added to the MER website:

http://mars.jpl.nasa.gov/mer/mission/spiritrightnow.html

The page will track the position of Spirit (formerly MER-A) from Earth to Mars until arrival at Mars in January 2004. Five views are currently provided and are updated every 10 minutes:

• Overhead view of the inner solar system showing the spacecraft's trajectory from Earth to Mars, and the spacecraft's current position.
• Mars as seen by Spirit (Mars will get bigger as the spacecraft approaches)
• Earth as seen by Spirit (large view of Earth currently being displayed)
• Looking down on Spirit (a closer view of Spirit's position)
• Looking down on Earth, showing the spacecraft's position relative to the Earth-Moon system.