Nowadays most of photographer use the APS-C (APS-C stands for Advanced Photo System type C) camera to capture the photograph. The reason because full frame camera is more expensive, especially for digital SLR. Size of APS-C sensor is smaller compare to full frame camera sensor, you can see more detail about APS-C here: http://en.wikipedia.org/wiki/APS-C
The picture above show the difference between APS-C camera (1.6 crop factor) and full frame camera (1.0 crop factor) when you take a photo. When you want take a landscape photo, you will know the difference between APS-C and full frame. For example you use EF 17-40mm f/4L USM with EOS Rebel Xti(1.6x) and EOS 5d(1.0x), you will know that EOS 5d will give you wider landscape. In this case if you use APS-C camera, you need to buy ultra wide lens, such as EF-S 10-22mm f/3.5-5.6 (only can be used for APS-C camera), tokina 12-24mm f/4, etc.