Here's what we have so far. What would you like to add? (It seems that some of your suggestions overlap what we have right now)
Categories:
2D Objects
Actions
Backgrounds
Blog/Site templates
Brushes
Clipart
Fonts and dingbats
Gradients
Icons
Layers
Stock photography
Tubes
Vectors
Wallpapers
Other
Formats:
.gif
.jpg
.png
.psd
-Jake