Last night Apple released iTunes 7.7 which features updates to make the iTunes App Store available. After updating you can access the iTunes App Store by searching for applications. It has not yet been added to the main iTunes homepage, but you can currently browse and download applications if you wish.
Click Here to launch the App Store in iTunes 7.7.
Apple also released an update for the AppleTV. The latest version of the software is available now and adds support for the new iPhone/iPod Touch remote application that is available for free in the App Store.
MobileMe was up briefly this morning, but has since been taken down again. Currently the Mac.com homepage shows a maintenance message.