I have a Samsung Syncmaster 204b. Its ~20inch at 1600x1200 resolution. Holds 4 tables perfectly. cost about 325.
Also i have second monitor hooked up to my computer which is my old one and only 19 inches at 1280X1024. You can get a video card that supports dual monitor for under 100 bucks and instally it pretty easily and use your old monitor as well as the new one.
Dual monitor is great because you can have 4 tables on one screen and have a webrowser and aim, etc on the other one.
Here is my setup with the samsung in the middle. My laptop is on the stand to the left and i dont really use it.
link incase pic doesnt show up