The buses services around the Cote d'Azur are great - I've taken them a few times during various jaunts to the area and been amazed at what you get for a basic 1€ ticket. From Nice Airport, you have 2 options for buses - the 1€ Cannes RN7 (bus number 200, around 90mins journey time along the coast) or the ~15€ "Aeroport Express" (bus number 210, around 50mins journey time via the highway).
Here is a link to the timetable, route and departure location info for all buses departing from Nice Aeroport (might be worth saving the Bus 200 and Bus 210 pdf's to your phone / laptop / ipod). Below is a screeny from the Nice Aeroport website with some basic info on the Bus services to Cannes.

UPDATE Hit the comments for direct links to the Bus 200 timetable and route info PDF. Thanks Anonymous, and sorry to hear you won't be there.