All different kinds of cleats, together with pedals - check out some of the sub-categories on the left if you are looking for specific types like SPD, Speedplay, Time, etc. Remember, if you are buying mountain bike shoes or road bike shoes you need to make sure the shoe type and the cleat type matches the pedal type. To try to simplify things, if you're just starting out with clipless pedals, there are several major types, and quite a few not-so-common types. There are three basic components to a clipless system - the shoes, the cleats (which are the clips that go on the shoe to attach it to the pedal) and there are the pedals of course. Bike shoes usually come with grooves or some other mechanism by which the cleat is attached to the shoe, and they are not all compatible. Do your research before buying a shoe - check which system it uses first and make sure you can attach the cleats pertaining to the pedals you are using. The most popular variety of pedal/cleat combination, especially in mountain-biking is SPD, and if you stick with this you won't go wrong, especially if you're a beginner. For road biking, the 3-bolt "LOOK" type system is common too. Many mountain bikers favour more exotic systems like the Crank Brothers "Egg Beater" type, which offers certain advantages over the SPD type - the action of clipping and unclipping is broadly similar, but the mechanism is very minimalist meaning you have four "points of entry" when clipping in (less fumbling), they are lighter of course, and they are much less prone to getting clogged with mud, which can be a big problem with SPDs.