Where should the icon to the mobile menu be placed?

I had a client bring up a good point recently about a mobile menu, specifically where should the "hamburger" icon be placed?

In looking at sites you see it in three common places, top right, top left or wherever the menu appeared on the site, typically below the logo and any header type content (login, cart, etc.) but above the main content of the site.

Where is the ideal place to place this icon from a UX perspective?

Note: This is for a mobile friendly website.