There is, for example, the RayCar demo for how to create good character and arcade car behaviors for the ODE physics engine. It uses DirectX with shaders, too, although you wouldn't know it from just looking at it :-) However, a physics engine example does not a full game make.
There are also a large number of test projects, anything from learning GLSL, to trying new approaches in networking, to testing out third party gaming engines. None of those end up in something I can actually put my name on and release, much less charge for. They do, however, end up in me learning more about the art and science of crafting games on modern hardware, as well as serve me well at work, pioneering "serious virtual worlds."
However, for some time, I've had this idea for a game which will bring certain kinds of people together. These people have access to computers, but aren't your typical target group for "AAA" titles. These people are social, and share a passion for the main theme of the game -- and they number in the tens of millions in the US. Currently, there is no online game which caters to these people. I want to fill that niche. I have artist friends who want to fill that niche. Maybe I can also make some money out of it, although that's really secondary. Break-even, enough to support servers and a self-sustaining community, would be a wonderful end result.
I won't share the theme just yet. Not because you'd steal my idea (after all, because it's not "AAA" you wouldn't be interested anyway), but because you'd laugh at me :-) If I ever get a "first playable," you'll be the first to know.