Google has a nice tool to check how much area of your webpage appears on the browser without scrollbar on different screen resolutions. Its helpful to ensure that most important parts of your webpage are located in the sections which are visible 100% of the users.
To view your own Web site with this same visualization overlaid on it, simply type its URL into the "Enter URL here" textbox at the top of the window and click Go.
Go - http://browsersize.googlelabs.com.