The Raspberry Pi has set the price bar very low for a fully functional PC, and no one has managed to get anywhere near it yet. VIA is within spitting distance though, with the announcement today of a $49 Android PC (APC) system.
Just like the Raspberry Pi, the APC ships as just a board without a case. It takes the form of a Neo-ITX motherboard that you can just plug into a TV or monitor, hook up some peripherals and start using. And it is tiny, measuring just 17 x 8.5cm.