A while ago I had a late, brief post on the ESA's SUCCESS contest for students.
Now, Space-for-All has an article on the opening of this year's SUCCESS contest, where the prize is a year-long internship to develop an experiment for the ISS. The details are here.
Space-for-All also points out an essay contest where the prize is a trip to watch the Space Shuttle launch of the Columbus ISS module. The topic of the essay is 'The value of human spaceflight for European citizens'. Check out the contest poster.
Both contests are open to students up to the Master's degree level.