A Kuro5hin poster has written a great detailed, illustrated tutorial on one-handed card-shuffling and deck-cutting. I have tried to learn to do this on no fewer than six separate occasions, but have always been stymied by my accursed stubby fingers.
From the basic grip rotate your hand so the deck is standing vertically along the longest axis, holding the cards up with your little finger resting underneath. The vertical grip isn't strictly necessary, but it makes a clean cut of the cards easier. Bring your forefinger out from the back of the deck and grip the side of the deck above your middle finger. Use your forefinger to pull back half the cards. Now pinch the bottom half of the deck (closest to your palm) tightly between thumb and forefinger, letting the top half go with your thumb and balancing it on your little finger and supporting it with your middle and ring finger. You'll want to rotate your hand away from you slightly to do this, letting the top half of the deck balance neatly in your last three fingers.
(Thanks, Jim!)
Update: Jer sez "I thought the instructions were good, but I think they'll be easier to
learn with the addition of the video I just shot of me doing them."
