Creating a software manual. Any supporting packages?

Though I don't know any packages that include symbols of radio buttons, check boxes, etc. I know some good GUI mockup software. I'd recommend using standard figures from mockup software, like the Pencil Project. It's licensed under GPLv2, and I think figures from mockup software are pretty straightforward. You could even use those graphics as inline images using a simple raisebox ensuring correct vertical alignment like this:

\raisebox{-0.5mm}{\includegraphics{button.png}}

For code snippets you could use the listings package, and for key-press sequences the keystroke package.