If you need a suggestion, then I'd say grab up one of the Asus LED monitors. Most of the good ones can be picked up for ~$150. They have amazing brightness and contrast for trading. I spend $400 for 4x21" monitors (1 LCD and 3 LED's). Gives me a total resolution of 7600x1080. If you go with something too small, you'll end up wasting excess PPI resolution.