I've been following the discussion about this on the Unmanned Spaceflight forums and it's a very perplexing problem.

They've discussed all kinds of possible solutions but I think in the end it's going to come down to using huge amounts of propellant to shave large amounts of speed off the lander before it really hits the bulk of the atmosphere and then having a giant heat shield to help lose the rest before parachutes, retros, or gliding can be of use. The engineering problems of transporting such a craft to Mars are going to be immense.

Anyway you look at it, it's going to be costly and on a scale we've never seen before. I truly hope they can solve these things in my lifetime.

Art