I'm a little surprised no one mentioned WebOS; the phone runs Linux and the PDK is in C (although as pointed out in the reply below, the PDK is only available on Windows and Mac right now).

I would also look at Meego (what Maemo became after it merged with Moblin), which you can code in C, C++, or Python (or really anything, although the native graphical interface is Qt).

The only issue with either of those is that you might be writing an app that no one will use (as one platform was still-born, and the second isn't yet born). That's the price you pay to avoid learning new technology though.