Sass Mixin for background-size: cover property. Includes IE support.

bg-cover-mixin.scss

// $bg-img-path: '../path/to/image.jpg'
// $bg-options: options are css background properties (ex. no-repeat center center)
@mixin bg-cover($bg-img-path, $bg-options) {
  background: url($bg-img-path) $bg-options;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
  filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src='#{$bg-img-path}', sizingMethod='scale');
  -ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='#{$bg-img-path}', sizingMethod='scale')";
}