You think landing on Mars was hard? Try landing on Titan–which is exactly what we’ll be doing, by very remote control, a little less than a year from now.
Good rundown here on the Cassini/Huygens probe that’s finally approaching Saturn; it should arrive this July. The Huygens probe will attempt to land on Titan, Saturn’s largest moon and the only satellite with an atmosphere, next January. It’s arguably the most ambitious unmanned space mission ever.