Check out the wood owl bits. Note that there are two (or more?) types. The "nail chipper" does not have spurs. The one you want is the "ultra-smooth".
http://www.timberwolftools.com/tools/woodowl/woodowl.html I've also heard good things about the 2-spur version that Gary sells:
http://www.timbertools.com/Products/HolzMaster_doublecut.html We do use the nail chipper version on site to pierce the tenons after assembly. They require less effort after the screw tip hits daylight.
