jQuery + OpenLayers

HTML

<script src="http://openlayers.org/dev/OpenLayers.js"></script>
<div id="map"></div>

CSS

#map {
  width:100%; 
  height:512px;
}

JavaScript

var map = new OpenLayers.Map("map");
var osm = new OpenLayers.Layer.OSM("OpenStreetMap");

var sedac = new OpenLayers.Layer.WMS("Population Density", "http://sedac.ciesin.columbia.edu/geoserver/ows", {
    layers: 'gpw-v3:gpw-v3-population-density_2000',
    transparency : true
},{
    opacity: 0.5, 
    isBaseLayer: false,
});

map.addLayer(osm);
map.addLayer(sedac);
map.addControl(new OpenLayers.Control.LayerSwitcher());
map.setCenter(new OpenLayers.LonLat(0, 0), 2);