What specs to look for in a good lcd monitor for computer/ps3?

im planning on buying something like maybe 24"or higher, and its gunna have an hdmi output, but i need to know, why there are so many prices, like i see the same size but is it the brand name that makes this difference? and i need monitor mostly for games and movies. thanks for any help, also what numbers do look for like aspect ration and all that idk wat u call it