For modern browsers like Safari 3 (or later), Chrome, Opera 10+, Firefox 3.6+, and Internet Explorer 9, you can use background-size like this:
body {
background-image: url(bg.jpg);
background-size: cover;
}
Here, cover means stretching the image either vertically or horizontally so it never tiles/repeats.
For lower versions of Internet Explorer, try using the below CSS code:
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src='.myBackground.jpg', sizingMethod='scale');
-ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='myBackground.jpg', sizingMethod='scale')";