I added a few more images to my 16 x 16px icon set.
How to grab doctype graphics from Apps in OS X
I found it really quick and easy to grab the doctype icons in OS X and make PNGs. If you want to do the same for yourself, you can follow these steps:
1. Navigate to your system's Applications folder using the Finder.
2. Right-click or Control-click the application whose icon you want to get, and select show package contents.
3. Navigate to the Resources folder and look for .icns files. For instance, the Garage Band app's icon is in /Applications/GarageBand.app/Contents/Resources/GarageBand App.icns. In the Finder's column view, you can preview the icon.
4. Copy the icon to another directory and close the application's package view.
5. Open Terminal and use the following command to convert the .icns file to a .png image file:
sips -s format png /Path/To/Icon.icns --out /Path/To/Converted Image.png
Done. OK, it's not that quick, but it's easy.