You can pick up aftermarket streaming devices but they are a) not cheap and b) a bit spotty.
Look at the Silicon Dust offering,
HDHomeRun DUAL - Generation 4 - US - Watch Streaming TV Anywhere
You'll still need a PC at the TV, unless it's a Smart TV that supports DLNA streaming.
A PlayStation 3 will work.
You could also go Raspberry PI, cheap and comes with OpenElec as a an OS option but the PI is painfully slow on channel switching, menu navigation etc....