There are five main types of sandpaper available, but not all are conducive for woodworking. Glasspaper, also known as flint paper, is very lightweight, typically a pale yellow color.
Glasspaper disintegrates easily, and is rarely used for woodworking.
Garnet paper is usually a brownish-red color, which is commonly used in woodworking. It will not sand wood as quickly as other sandpapers, but leaves a better finish. Garnet is an excellent choice for finish sanding.
Aluminum Oxide is another common type of sandpaper for woodworking projects. It is the type of paper most often used in power sanders. Aluminum Oxide is more durable than Garnet paper, but doesn't leave as nice of a finish.
Silicon Carbide paper is typically a dark gray or even black. This type of paper is used primarily for finishing metals or for "wet-sanding", using water as a lubricant. While some advanced finishes use Silicon Carbide paper, it is not typically used in woodworking.
Finally, Ceramic sandpaper is made of some of the most durable abrasives available, and can remove considerable amounts of material in a hurry. Ceramic paper is often used for belt sander belts, but sometimes is used for hand shaping of wood. It will usually leave a very rough finish, so exercise care when using Ceramic sandpaper, particularly on plywood and veneers, where it can quickly sand through the finish layer and ruin a piece.