Most people think of a Prefold when they thin cloth diaper
There are Chinese Prefolds and Indian Prefolds, Hemp flats etc. There are also contours.
They typically come in 3 sizes. These are the rectangular cloth diapers that need to be properly folded and secured with a pin or snappi.
Be sure to get a diaper cover to avoid leaks!
Then there are fitted diapers (they also need covers unless they are AIO all in one)
Fitted diapers have a contour shape a have a gathered (elastic) edges around the legs. You can secure these with snaps, velcro, aplix or touch tape. These can range from $22-$40
Here are some fitteds http://www.thegoodmama.com/index.php?main_page=index&cPath=71_97
AIO all in ones
They are fitted diapers that have an outer waterproof layer. (PUL) Often they have fewer absorbent layers than their counterparts. These diapers tend to be used when you go out. They are not practical for daily use since frequent washing and drying reduces the effectiveness of the waterproof outer layer. Here are some AIO http://www.muttaqinbaby.com/catalog/zen-cart-v1.3.6-full-fileset-10272006/shop/index.php?main_page=index&cPath=2 AKA Mutts
Bum Genius AIO AKA BG AIO http://www.cottonbabies.com/product_info.php?cPath=28&products_id=1811
Pocket Diapers Pocket diapers are two piece diapering system typically with a piece of fleece that makes up the inner portion of fabric and a waterproof layer that makes up the outermost portion. An absorbent material is stuffed inside of the two pieces making it an all in one. These are quick drying as they are washed and dried as separate pieces. If you have a heavy wetter you can add more stuffing. Happy Heiny's are pocket diapers http://www.onesizediaperstore.com/-Happy-Heinys-One-Size-Get-me-Started-Package_p_17.html These are also one size diapers, not all HH's are one size.
One Size Diapers
These are designed to fit a newborn until they learn to use the potty. The snaps are located just below the fasteners with tops and bottoms lined up vertically. This allows you to adjust the size of a diaper as the baby grows. This feature of fitted or pocket diapers allows you to purchase fewer sizes. You have seen some already in the Good Mama and Happy Heiny so I'll show you a Bum Genius One Size All In One http://www.onesizediaperstore.com/Bumgenius-One-Size-Organic-Cotton-All-in-One-Diaper_p_80.html
Just like the name says. It covers your diaper. It is the water proof barrier that protects the world from what is inside the diaper. http://www.cottonbabies.com/product_info.php?cPath=36&products_id=1610
Wool and Fleece are popular choices. Wool and polar fleece are water resistant, rather than waterproof. They do allow some wetness to wick through from the diaper but still manage to keep babies' clothes dry. The wool has a different way to be cared for rather than being thrown in the wash.