In addition to a handful of new Chromecast-supported apps announced by Google, Sling Media is getting in on the action. According to this blog post, the Slingplayer app for Android smartphones now has Chromecasting capability. Though the latest update for the app itself was way back in July, Chromecast support is often enabled via a server-side switch, so it should be working now. Compatible Sling hardware includes the Slingbox M1, 350, 500, and SlingTV.
The long awaited Sling Player Mobile application is now officially available on the Android Market, with download numbers <50 (i.e. moments ago).
Sling promised the app would go live tomorrow but pulled the trigger early and launched it today instead (though I guess it is tomorrow in some time zones).
Update: their Android page is now live.
Things are looking good - so far all 3 reviews are 5 stars, though this may change when we get more installations.