As one of the primary points of contact on your bike, saddles are an extremely important component and can mean the difference between a fun day out on the trails or an agonizing night thereafter. But unless your local bike shop is willing to let you test out different models, it can be extremely difficult to know which one to purchase. Generally speaking, if your bike is one that requires you to lean forward, you'll want a narrow saddle. As your riding position becomes less aggressive, the more you'll want a wider saddle, to distribute weight.
Take for instance the Bel-Air, from SDG Components. With a decade of proven design and a track record of success, this saddle is a safe bet if your riding style requires an aggressive stance (which is the case for most downhill, cross-country and trail riding). It has a slight, 3/4-cut channel groove to relieve pressure and is made of a medium density foam to provide the perfect blend of comfort and power transfer. The Bel-Air works extremely well for a wide variety of riders and applications, from DH to XC to road to BMX.