Canon and Nikon are the two giants in the field, but there are several other quality dSLRs that you may want to look at.
Canon offers a complete line of cameras, lenses, flashes, and other accessory products as well as photo printers.
Nikon has a complete line of cameras, lenses, flashes, and other accessory products and scanners.
Olympus is the primary maker of 4/3 camera systems, including a full line of lenses, flashes, memory cards, and photo printers.
Pentax has several models of digital SLRs along with a wide line-up of lenses. You'll also find flashes, light meters, and other accessories.
A Pentax by any other name would likely be the Samsung Digimax. Both camera systems offer the same features and accessories.
Sigma makes the SD series of digital SLRs which use the Foveon sensor (covered in Chapter 1). They also have a complete line of lenses and flash accessories.
A year ago, this would have been Konica-Minolta. That highly respected brand is now marketed by Sony under the Alpha label. A full line-up of lenses, flashes, and accessories are available for the Alpha.