Guitar Hero 5 -- here in the States, folks who purchase the game are eligible to receive Guitar Hero: Van Halen for free. However, in the United Kingdom, the offer is incredibly sweeter -- those who pre-order Guitar Hero the Fifth through Amazon can also grab Guitar Hero: World Tour for the low, low price of nothing.
OXM received instructions from Amazon.UK on how to utilize the offer -- simply add Guitar Hero 5 (on any platform) to your basket, then add the special promotional version of World Tour for the appropriate console. Go to checkout, and the price of the latter will magically change to zilch. If only this kind economic wizardry applied to every purchase in our life.