There are many hostels in or around Geneva centre, however there are always long waiting lists and you must almost always reserve a room long in advance.

You can find further information through this links:

http://www.fasngo.org/accomodation.html

http://www.easywg.ch/?l=1

http://www.cityhostel.ch/site/fr/

http://www.genevahostel.ch/en/

http://www.hostelz.com/hostels/Switzerland/Geneva

http://homestpierre.ch/