Deezer is a freemium streaming music service with over 30 million tracks, but it's not available in the US. It's free with some ads and limited skips, but now you can cast from it. Daily Burn is free, but it's less fun. Well, unless you're one of those people who insist that exercise is fun (it's not). This one streams workout videos to your TV with Chromecast support. Then there's the PBS Kids app, which you can probably figure out. It streams kids shows, and it appears to be a new app.
All three apps are casting as of today's updates. Not bad for a $35 dongle.