www.runmfd.com
thinking of picking some up for myself. I'm in the same boat and since I already have some bindings that would work with them, they seem like the best bet. Based on some research, they don't appear to affect the ski's flex any differently than a regular binding.
You can also check out alpine trekkers (which seem to have a big problem of breaking fairly easily) and dukes, barrons, whatever, but apparently they put you kinda high above the ski and are relatively heavy (though not much different from a binding + mfd plate).
Then, of course, if you wanna go all out, you can look at fritschi, etc, and a get full boot/binding setup, but some say they can't hold up if you push em real hard, and they're certainly more expensive (unless you're in the market for new boots, as well, but those boots are more optimized for the uphill, so they lose some downhill functionality).
All in all, the run MFD setup hasn't really been seriously put to the test (at least by full-on public distribution), but it seems like a really good option for those who want a fully-functional ski in the resort, as well as a touring ski with a fully-functioning binding in the backcountry.
