This is my latest toy. It's a Contour ShuttlePRO v.2, USB interface, 15 customisable buttons (plus jog/shuttle), a shed load of application pre-loads, plus import/export on your custom settings whenever you take it anywhere else.
In Avid, the inner dial will move your playhead along one frame at a time (at just the right sensitivity), and the outer will play your video at normal speed, increased speed, reverse speed.... basically the same as tapping the J and L keys multiple times, but in a far more ergonomic and inutitive way. One minor grumble that there's no lock to keep the video playing at normal speed as you'd get on a Steenbeck or a Lightworks console, but it's easy enough to adjust your hand and/or map a button or two to the relevant function.
I've put it on the left of the keyboard so that I can simultaneously use the shuttlepro and the mouse, though I'm not sure it's possible to entirely omit the need for the keyboard - I have settings for digitising, assembling/ editing and trimming (see below the cut), and rather than go up to the drop down menu to select the exact setting I need for a certain splice, it's easier to just press the corresponding key.
I'm still changing some of the settings and buttons since I got it a fortnight or so ago to find the best positions and keystroke replacements, but so long as I remember it's there I've found that my editing speed has significantly increased as I've become more used to the shuttlepro interface. I'd definitely recommend it - and for video editing, the 15 button shuttlePRO is a must - its smaller cousin the ShuttleXpress has just 5 buttons in addition to the jog/ shuttle wheel, and finding your way around the larger version isn't as intimidating as it may look at first.