The Apple Store is down for maintenance. It is Monday though, not Apple's favorite day for new product releases, which is Tuesday. Still, chances are high that Apple will start selling OS X Snow Leopard in the Apple Store today.
Update: Snow Leopard now available in the Apple Store, release date August 28th
You have been able to pre-order Snow Leopard from Amazon and others for a while, but Apple did not offer it yet.
Of course there is always the chance that there will be nothing new in the Apple Store, when it goes back online again.
Check the Apple Store.
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