<<>Two. I want to experiment with some halftones, and
>know that they come in little sheets that you can cut
>apart and apply or maybe rub on, but can't think of
>where I could buy them or what they're called.
Zipatone is the classic name; I think these days it's Lettraset.>>>
For anyone who hasn't found this wonderful resource for comic art supplies:
www.bluelinepro.com
I believe they call them professional artist tones or something to that effect. they even have the hard to find manga tones.
And, as was said, there are many online tutorials for creating half tones in a program like photoshop.
-shane