A boilerplate or starter template of media queries for various device widths and orientations.

media-queries.css

/* Smartphones (portrait and landscape) ----------- */
@media only screen and (min-device-width : 320px) and (max-device-width : 480px) {
    /* Styles */
}

/* Smartphones (landscape) ----------- */
@media only screen and (min-width : 321px) {
    /* Styles */
}

/* Smartphones (portrait) ----------- */
@media only screen and (max-width : 320px) {
    /* Styles */
}

/* iPads (portrait and landscape) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) {
    /* Styles */
}

/* iPads (landscape) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : landscape) {
    /* Styles */
}

/* iPads (portrait) ----------- */
@media only screen and (min-device-width : 768px) and (max-device-width : 1024px) and (orientation : portrait) {
    /* Styles */
}

/* Desktops and laptops ----------- */
@media only screen and (min-width : 1224px) {
    /* Styles */
}

/* Large screens ----------- */
@media only screen and (min-width : 1824px) {
    /* Styles */
}

/* iPhone 4 ----------- */
@media only screen and (-webkit-min-device-pixel-ratio : 1.5), only screen and (min-device-pixel-ratio : 1.5) {
    /* Styles */
}

Taken from @chriscoyier whom adapted from Andrew Clarke