2em.ch, rental of cars directly from locals and not from companies. :) 
The cheapest option that also lets you meet some local people! 

Interesting- thanks for the suggestion. Sadly quite a bit more expensive as they charge mileage on top though, could be worth it for shorter trips.

Not the cheaptest, but I have used Avis on Rue du Lausanne on several occasions and everything was great, their cars are always new and clean and it's very easy to pick up and return the car. I always book online, and if you book in advance you might get some really good prices. Now is the high season so the prices are very high, if you book after a month or two you might get a car for 45-50 CHF per day.