Google would love for you to put a Nexus 7 under someone's tree this holiday season, but they also don't want anyone who can't part with $229+ at the moment to feel left out - so they're now offering customers who purchase a Chromecast from Google Play with a free HD movie rental. If Play Movies isn't quite your cup of tea, you're also free to take $6 in Play Store credit instead.
Update: Google has updated its Play gift card support page to reflect this change, and this change hints that at some point this feature might allow you to gift Play Store credit:
Thinking about picking up a Nexus 7? You might want to get on that before the end of this month (right here), as the $25 Play Store credit promotion Google announced with its slate at Google I/O expires on September 30th. That means you must redeem the promotion before that date by signing into your Nexus 7 with a Google Wallet-linked Google account (that has a credit or debit card on file).