Canon 5D tips posted a gorgeous timelapse video of New York. The video used a fantastic tool called the the Little Bramper. It allows you to bump your exposure when needed over time. This obviously comes in handy for timelapse photography. They claim it works with both the 5D markII and 7D.
Check out the Little Bramper website for more info on how it all works. The timelapse they have in their promotional video is incredible. Using this, it seems you can make some amazing timelapse videos. Very cool stuff.