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!