I was trying to figure out a way to prevent the audible gmail notification from sounding for new mail from a few mailing lists. I figured out a way which works but may be less than graceful. I set up a few filters in gmail itself via Settings -> Filters to mark emails with certain keywords in the subject line as read upon arrival. I still see the new email on my droid in the gmail app, however it shows read and no longer triggers the audible notification. To draw attention to it however, I setup a dark colored label for this mail. Works for me.