Does anyone know if there is a website that shows you where you can get the best price deisel and petrol?

Best petrol prices you're likely to find.

I know for a fact, the petrol kiosk at Baden-Datwill Macdonalds is 3-6 rappen cheaper than those in ZH.

Tamoil is also the cheaper lot.
Shell is the most expensive.

I also think it is illegal /not allowed (for the oil cartels and petrol stations) to publicise their prices online for comparison.

Thanks but it's a bit of a schlepp from Lausanne