(This dates from a while back and if it's been posted already a mod may remove this thread)
On this website you find true color images taken by the Panoramic Camera on each of the Marsrovers Spirit and Opportunity. This is how images would look like, if an astronaut on the surface of Mars took images with a 1 Megapixel digital camera and sent them back to Earth via a planet wide Internet. That means, the colors appear the same as the astronaut would see them.
On the left you see two columns of number pairs. The number before the colon represents the Martian solar day (Sol) since the landing of each Rover. The link leads to an album page with almost all color images taken on that day. The number behind the colon is the number of images available on that album page.
Note, that the color images are created automatically from all raw color data available. That means, there are also images which do not represent true color as they have been taken with filters outside the wavelength range of the human eye.
You'll see Mars isn't red at all
Give it a try at: http://areo.info/mer/