ESA and NASA have formalized their relationship to explore Mars through a series of joint missions in the mid to late coming decade. (See story at BBC http://news.bbc.co.uk/2/hi/science/nature/8348867.stm ).
ESA is expected to provide a billion euros (~$1.4-1.5B depending on currency fluctuations). No mention is made of NASA's contribution, but based on current budget projections, NASA is likely to contribute several billions of dollars.
The planned missions are as described previously in several blog entries:
2016 - ESA provided orbiter with NASA launch to study trace gases. ESA will also provide a lander that will demonstrate landing technology and carry a weather station. No mention of how long the instruments are expected to function.
2018 - ESA and NASA rovers carried to the same location by NASA's skycrane landing system.
2020 - A network mission is under consideration.
Editorial Thoughts: This would seem to lock in the 2016 and 2018 into NASA's plans for the next decade. The Decadal Survey in progress is specifically limited to proposing missions beyond currently committed missions. By the time of the 2012 Decadal proposal a number of missions are likely to be in that category: the 2016 and 2018 joint Mars missions, the Jupiter Europa Orbiter,a to be selected New Frontiers, and a to be selected Discovery mission. (I'm probabably missing a mission or two. I haven't included missions expected to launch by or within a year or so of the report.) The actual budget left for the Decadal Survey to work with may be fairly small. By my rough accounting, the list above could be in the neighborhood of $7B (before cost overruns) out of an expected decadal $12B.