If you are looking for summer housing, check out the following links :
http://www.unige.ch/dase/bulog/form/bourse.php (the UNIGE housing- I found this to be the most useful!)
https://espace.cern.ch/hostel-service/Wiki%20Pages/Hostels.aspx (the CERN hostels- they are expensive!)
https://espace.cern.ch/cern-market/default.aspx (click on housing on the left and login with your cern account)
Best of luck!