NexGenWars.com is a site that updates the number of consoles sold for each of the nextgen consoles. How accurate it is I am uncertain, but its better than nothing and they have some cool images that you can add to your site or forum, myspace, etc for those fanboys out there.
Below are the images and the number of consoles sold is on them.
Here is what NexGenWars.com have to say about their site:
The next generation of gaming is upon us, and the console wars have begun. NexGen Wars.com has spent countless hours researching sales facts from dozens of sources to track the worldwide sales of the consoles and monitor the next generation of console wars between the Microsoft Xbox 360, the Sony Playstation 3, and the Nintendo Wii. Remember, these numbers are only estimates, but they are constantly monitored and updated to assure the closest estimates possible for the Xbox 360, Playstation 3, and Wii.
They claim elsewhere on their site that they are updated once every minute.