Block Mixins (sass 3.2). You can use these like:

_screens.sass

// defines some media block mixins for use
// 
//  e.g.
//  +phone-landscape-and-down
//     float: none
//     margin-left: 20px
//

$media-phone-landscape: 480px
$media-tablet-portrait: 768px
$media-tablet-landscape: 980px

@mixin tablet-portrait-and-up
  @media only screen and (min-width: $media-tablet-portrait)
    @content

@mixin tablet-portrait-and-down
  @media only screen and (max-width: ($media-tablet-landscape - 1px))
    @content

@mixin tablet-landscape-and-up
  @media only screen and (min-width: $media-tablet-landscape)
    @content

@mixin phone-landscape-and-down
  @media only screen and (max-width: ($media-tablet-portrait - 1px))
    @content

@mixin phone-portrait-and-down
  @media only screen and (max-width: ($media-phone-landscape - 1px))
    @content

@mixin tablet-landscape
  +tablet-landscape-and-up
    @content

@mixin tablet-portrait
  @media only screen and (min-width: ($media-tablet-portrait)) and (max-width: ($media-tablet-landscape - 1px))
    @content

@mixin touch-disabled
  body.touch-disabled
    @content

@mixin touch-enabled
  body.touch-enabled
    @content
      
@mixin phone-landscape
  @media only screen and (min-width: ($media-phone-landscape)) and (max-width: ($media-tablet-portrait - 1px))
    @content

@mixin phone-portrait
  +phone-portrait-and-down
    @content

@mixin retina-only
  @media only screen and (-webkit-min-device-pixel-ratio: 2)
    @content