I've created my first extension, called Ultimate Fullscreen. People seem to be pretty happy with it, and suggested I create a new thread for it here.
The Ultimate Fullscreen object allows you to make games in fullscreen without changing the resolution mode, while maintaining aspect ratio. Your game can be any resolution. Widescreen games are displayed in letterbox on normal screens, and non-widescreen games are displayed with black bars on the sides. Pixels are crisp and not anti-aliased.
There are also options for pixel-perfect scaling (integer-only scale), Hor+ and Vert- widescreen, and manual control of the game rectangle.
Included is an example showing off the capabilities of the object.
If you're not totally sold on installing the extension, you can just download the example EXE.