This app allows you to toggle between ring mode and vibrate mode either by using the right slider in the lock screen or selecting silent mode from the menu you get by long pressing the power button. Tested on a N1 but I see no reason why it shouldn't work on other devices.
Added ring mode togling from the notification area. Due to this I had to bump the minimum SDK requirement to 1.6 (Donut). I'm working on preventing the icon from showing up in the status bar but I have yet to find a good clean solution that I like.