11-22-12 Update Snow Leopard 10.6 is once again available from the Apple on-line store via this link.
The day after Mountain Lion (OS X 10.8) came out, Lion (OS X 10.7) and Snow Leopard (OS X 10.6) were no longer available for purchase, not even at the Apple on-line store. This can be a problem for late adopters with Macs that can run Lion, but CAN’T run Mountain Lion.
Some Mac owners have yet to upgrade to Snow Leopard, which you need to install first in order to get the Mac App Store and upgrade to Mountain Lion. Sort of a Catch-22! There are also a large number of Mac owners with legacy Apple hardware (like early Mac Minis, the first MacBooks, and Intel iMacs) that are still running Tiger (Mac OS X 10.4) who need to finally upgrade to 10.6.8 in order to keep using their computers with the Internet.
Thankfully, you can still buy Snow Leopard and/or Lion, and you don’t have to pay the $80 to $100 going price on Amazon. Just call Apple Telesales at 1-800-MY-APPLE to order it over the phone. You can buy the single-user or the family pack version of Snow Leopard 10.6, or you can purchase an App Store redeemable code for Lion 10.7.