I personally prefer cash, but Microsoft only gives a rebate for the Xbox 360 this holiday shopping season in the form of two pre-selected games.

The Forza Motorsport 2 and Marvel Ultimate Alliance will both be included with the Xbox 360 for $349.99 and with $449.99 Xbox 360 Elite. Both bundles will be available at game retailers by the end of October.
We are still waiting for the official announcement on the new lower priced $399 Sony PS3 console for the U.S. market. The current rumored date is November 2nd.

The biggest sales driver for the Xbox 360 is Halo 3 anyway. This game is Microsofts big ace for this Holiday season.
Via this announcement on the Xbox.com site.