Apple has launched the Mac App Store which allows Mac OS X users to purchase and download Mac software using their iTunes account.
Mac users need to update to Mac OS X Snow Leopard to version 10.6.6 (100+ MB download) in order to get the Mac App Store.
Like the iTunes Store, Mac App Store highlight apps that you might interested; Show you what’s hot and staff favorites; Sorts apps in categories and allows users to search for apps they want. And, of course, the Top Paid and Free apps charts.
Update: Since it is using iTunes account, the purchased apps on Mac App Store is following you wherever you are (another Mac computer of yours). You only need to re-download the apps, say on a brand new Mac. Sweet! (thanks, @tjunkie)