Retina

Detecting and using Retina Tiles
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Retina</title>
  <meta name='viewport' content='width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no' />
  <script src='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.js'></script>
  <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.css' rel='stylesheet' />
  <!--[if lte IE 8]>
    <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.ie.css' rel='stylesheet'>
  <![endif]-->
  <style>
    body { margin:0; padding:0; }
    #map { position:absolute; top:0; bottom:0; width:100%; }
  </style>
</head>
<body>
<div id='map'></div>
<script>
var map = L.map('map')
    .setView([37, -77], 5)
    .addLayer(L.mapbox.tileLayer('examples.map-20v6611k', {
        detectRetina: true
    }));
</script>
The code and documentation to mapbox.js is hosted on GitHub where you can contribute changes and improvements.