The classic SPD PD-M520 pedal is known by many mountain bikers and touring cyclists. This mountain bike pedal is the perfect pedal for those who just started with mountain-biking. They're not expensive to buy, but they are fitted with the same technology as the more expensive XT and XTR series. Of course the 520 pedals are a lot heavier and has bearings of less quality, but that's why the price is also very attractive.
The PD-M520 pedal has an open body so the mud doesn't stick to you pedal when you clip in. In addition, the spring tension is adjustable. You could put the spring tension on very low so it's easy to click out of your pedal or raise the tension to make it harder to clip out. The pedals come with the SH-M51 cleats that have 3 degrees of freedom of movement.