The Apple Snow Leopard OS X Update ships today. If you can wait a little bit then you can buy the Snow Leopard 10.6 OS X Update for only $25 on Amazon.com ($4 savings). Of course Amazon ships Snow Leopard for free.
You can save even more on the OS X 10.6 Family pack, Server and Box Set.
Do not expect the Apple Store to be giving you any rebates. If you can wait until next week to upgrade your Mac than Amazon has the Snow Leopard deals for you.
More details on Amazon.