How many man-made objects are currently on the surface of Mars? How many are still sending live signals? How many crashed & burned before they got there?
Viking 1 and 2 landed in the 70’s, and are both dead. The small pathfinder rover is there, but dead. Spirit and Opportunity rovers are still working. The Phoenix lander is there, but is now dead. Last contact was just before December. It’s now probably completely buried in solid CO2.
The Russian Mars 3 lander was successful in touching down, but it only transmitted for 20 seconds before dying. Mars 6 lost contact just as it was touching down, but the Russians believe it actually landed, so maybe it counts.
So 7 or 8 man-made vehicles are sitting on Mars. 9 if you count the platform for pathfinder separately. Only two are working.
In addition to the ones that successfully landed (mentioned by Sam Stone), there are a few other crash-landings that took place:[ul][]Mars 2 lander, August 1971, was first man-made object to reach the surface.[]The Mars Climate Orbiter broke up in the Martian atmosphere in September 1999, due to the infamous metric-Imperial mixup. There’s likely some debris from it on the Martian surface.[]The Mars Polar Lander crash-landed in December 1999. The lander vehicle also gave a ride to two surface-penetrator probes, the Deep Space 2 project, which also landed on the surface but did not send back any data.[]Beagle 2, a European project, may or may not have crash-landed on the surface in December 2003. Decepticons are rumoured to have been involved.[/ul]
In addition to the successful missions Sam Stone listed, there have been several unsuccessful landers:
Russia’s Mars 2 lander crashed, but it was the first man-made object to reach the Martian surface.
The US’s Mars Polar Lander lost contact with Earth during landing and it’s presumed to have crashed. Deep Space 2 had two probes that were designed to impact the surface at about 400 mph which would propel sensors a couple of feet into the ground to take measurements and samples below the surface. Contact was never re-established after landing.
Beagle 2 was a British lander that lost contact before its scheduled entry into the Martian atmosphere. It’s not known if it crashed - it may have missed Mars and ended up in orbit around the sun.
Not Mars itself, but next year Russia will be launching Phobos-Grunt, which will attempt to land on the Martian moon Phobos and return soil samples to Earth. Very cool!
<D’Oh! Mike posted while I was editing mine. 
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For a comprehensive listing, check out the Mars Scorecard in the Mars Expensive Hardware Lob. NASA’s Planetary Science – Mars webpage also has a detail listing of all NASA missions and a chronology of all Mars missions.
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