Apple has announced the grand opening of the new Mac App Store
Access to this store requires the just-released Mac OS X 10.6.6 available via the Mac OS Software Update function. Mac App Store should become available on the Apple menu once the update has been installed.
Aperture 3 is available at the Mac App store for only $79.99 in the US ($119 off regular price). Check your country's App Store as the deal varies by country. (thanks Adam)