I use these:
/* Non-Retina */
@media screen and (-webkit-max-device-pixel-ratio: 1) {
}
/* Retina */
@media only screen and (-webkit-min-device-pixel-ratio: 1.5),
only screen and (-o-min-device-pixel-ratio: 3/2),
only screen and (min--moz-device-pixel-ratio: 1.5),
only screen and (min-device-pixel-ratio: 1.5) {
}
/* iPhone Portrait */
@media screen and (max-device-width: 480px) and (orientation:portrait) {
}
/* iPhone Landscape */
@media screen and (max-device-width: 480px) and (orientation:landscape) {
}
/* iPad Portrait */
@media screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:portrait) {
}
/* iPad Landscape */
@media screen and (min-device-width: 481px) and (max-device-width: 1024px) and (orientation:landscape) {
}
http://zsprawl.com/iOS/2012/03/css-for-iphone-ipad-and-retina-displays/