Now that the Chromecast SDK is available to anyone, Vudu is working on being added to the list of apps that support it.
For anyone unfamiliar with Vudu, it is one of a few video streaming services that allows you to purchase movies. There are apps for it available for Android, iOS, Roku, PS3 and X-Box 360 (XBL Gold required). This would allow anyone that just has the app on their phone/tablet and a Chromecast to view their movies on any TV with an HDMI port (provided there's also Wi-Fi for connecting to it). Vudu is also one of the retailers for Ultra Violet digital copy. So if you redeem your UV code, even if you select a retailer other than Vudu (Flixster, Target Ticket, or Cinema Now, but not Google they're separate) if they're both linked to the same UV account you can still view it through Vudu
You can also apply here to be a beta tester and get access to it sooner. Even if you have a regular Vudu account, you'll still need to sign up for a separate beta account (which didn't seem clear to me). ETA: the signup is a PiTA process and even requires digitally signing an NDA, so I think I'll just wait for the official app update.