Compose sidebar needs the ability to easily grab files from my computer

It's nice that you can snag images from the web and other messages for sticking into an email, but it would be even nicer if I had the ability to search files and images on my computer in the same way.

The image browser in the attachments dialog is nice, but having something like that plus the ability to add other attachments that are on my computer directly from the compose sidebar would be killer.