A Graphics tablet is a device that is often used by professional artists or those in areas where a touch-up on pictures is required e.g magazine editors, games editors.
There are several differant types of graphics tablets, the best of which is argued to be made by, Wacom. They make graphics tablets that can be used as a tablet connected to a monitor and as a tablet with the monitor that is already integrated into the tablets system, a tablet that has this is the CintiQ.
The CintiQ is roughly about £1000. One of their newer models, the Bamboo is roughly going to be about £220. The prices of these differ as the CintiQ has an integrated screen whereas the Bamboo will not.
Some things to look for are the sizes of the tablets, is the tablet A6, which is the smallest a tablet can be, or is it A2, which is the largest a tablet can be. Also, how sensitive is the tablet? e.g when you press down hardly on the tablet, does the draw line become thicker? When you gently draw with the pen, is the draw line thin? The sensitivity of the tablet is important for whatever the usage is going to be; what you are using it for.
The bigger the tablet however, the better quality your getting for the money you spend.