Mountain or Road? I use Shimano's M540 pedal, a "mountain" pedal, which is wonderful, as good for most purposes as the more expensive SPD pedals and without the engagement/disengagement problems of the cheaper ones. (Shimano also encourages this pedal for century rides on the road). Don't pay more than $80 for it. Bear in mind that even for road, mountain pedals can work at the highest level -- evidently a stage of this year's Giro and the US Pro road championships in Philadelphia were won by a rider on titanium Eggbeaters, which are as pure a mountain bike pedal as can be.
Also bear in mind that the smaller the pedal-to-cleat area, the more rigid the shoe sole needs to be so that you don't feel the thing pushing through the soles of your shoes. For this reason, a mountain bike pedal used on the road over a long distance will be demanding of the shoe, because the cleat delegates its responsibility for pushing on the pedal to the sole of the shoe. A road bike pedal may mean getting away with a softer and therefore cheaper shoe, because the larger cleat shares duties with the shoe sole.