Michael Downes writes in praise of PowerGrips at Bicycle Design.
For those not familiar with PowerGrips, they're a lot like the old style clips and straps. A diagonal strap of slightly flexy fabric from the front of the pedal to the side keeps your foot somewhat secure on the pedal. Unlike clips and straps, however, a simple twist and pull of your foot releases your foot from the PowerGrips strap. Insertion is the reverse -- come in slightly from the side and straighten the foot into position on the pedal automatically cinches the strap tight. It's really pretty clever.
PowerGrips product review at MTBR.com.