Mars Rover Finds Rock Resembling Meteorites That Fell to Earth
http://www.jpl.nasa.gov/releases/2004/104.cfm
Opportunity found a rock on Mars that resembles meteorites found on Earth.

Standing Body of Water Left Its Mark in Mars Rocks
http://www.jpl.nasa.gov/releases/2004/90.cfm
The press release explaining that Opportunity could be in an area which was once the shoreline of a salty sea.

Mineral in Mars 'Berries' Adds to Water Story
http://www.jpl.nasa.gov/releases/2004/88.cfm
The press release on the berries found in an outcrop provide evidence that Mars had water at one time.

Volcanic Rock in Mars' Gusev Crater Hints at Past Water
http://www.jpl.nasa.gov/releases/2004/79.cfm
The press release announcing that Spirit found evidence of water at its landing site. The evidence was found in a very different rock than those in which Opportunity found water.

Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet
http://www.jpl.nasa.gov/releases/2004/74.cfm
The press release that detailed the evidence that Opportunity's landing site may have been soaked in water.

Modern Mars: Latest Spacecraft Findings Redefine Future Missions
http://www.space.com/scienceastronomy/modern_mars_040407.html
This article looks at the discoveries of Spirit, Opportunity and the Mars Express and the impact thoses discoveries will have on future exploration of Mars.