Answer:
The two current Mars rovers are Spirit and Opportunity. After Spirit became stuck in sand in 2010, contact was lost in December, 2010. Only Opportunity is still functioning. An earlier rover, Sojourner, explored Mars for 3 months in 1997.
NASA plans to send another rover, Curiosity, to the planet as part of the Mars Science Laboratory mission, due to launch near the end of 2011 and arrive on Mars in August 2012.