As from 1st July 2011, the prices of stamps in France are increasing.
It will be €0.60 for France (increase of 2 cents) and €0.77 for Europe (it is currently €0.75).
If the stamps you have at home don't show any prices on them, you can still use them. If they do have a price on them, you can get some 1 cent stamps.
For more information regarding the services offered by La Poste see this link here.