The Mac OS X Resolution Independence Utilities project is a Google Code project where utilities and code will be available for creating high- or multi-resolution imagery.
I aim to personally provide Cocoa examples and code, but this is labelled “Mac OS X” - code for Carbon, Java, X11 and OpenGL is welcome too (even though, for example, Java has an integer-based coordinate system). For contributions, the BSD license or more allowing licenses (like the MIT license or public domain) is required.