There is a very interesting talk by Jean-Pierre Bibring, Institut d'Astrophysique Spatiale, Orsay, France titles "Mars Exploration: Bridging Our Past and Future" given at the recent AGU conference in San Francisco.
Available for download at http://www.agu.org/meetings/fm09/lectures/videos.php
It is a one-hour talk and ~400Mb but it is very interesting covering such topics as when there may have been water on Mars (the Phyllosian period), the effect of the heavy bombardment comparing Earth and Mars, the loss of the Mars dynamo and consequent loss of atmosphere and water and the volcanic period with sulfates (Theikiian period). Lots of thought-provoking and probably controversial ideas but backed by chemical evidence.