If you're into 3D like me, chances are you would often play a game and wonder how you can extract those gorgeous game models and load them into your favourite 3D program. There are user or official apps that can do this, though most often than not it only works with a particular game and the workflow could be rather convoluted.
I came across a nifty app called 3D ripper DX when I was browsing through the CGtalk forums, . What it does is that injects itself into the game as you run it (you either launch the game through the app, or use a global monitor that runs in the background as you launch the game independently), and with a keystroke it will take a "snapshot" of the geometry and texture data in the current render call.
In its current version, it only works with DirectX 9 games and comes with a plugin for Autodesk 3DS Max only. If you are using other apps, fret not as it also exports to the wavefront .obj format, which should be compatible with almost everything else, although the obj export could be distorted and requires you to dig into the file to change some parameters. Another nitpick is that I can't seem to import the models with their UVs intact. I haven't gotten a chance to test the Max plugin because I don't have the software.
Be warned though, depending on what game you're running, the captured geometry could be quite heavy.
Of course, the assets you captured from any game are the intellectual property of their respective developers, so use it responsibly.