The NASA Earth Observatory published a series of 500-meter resolution satellite imagery in 2005, in true color showing seasonal dynamics at monthly intervals. This tileset is a free alternative to Bing Maps, and demonstrates how custom image tiles can be used with Polymaps.
This map is constructed using a single image layer pulling tiles from Amazon S3. (Hosting courtesy of the folks behind Modest Maps.) The tiles are in spherical mercator coordinates, and the map has standard interaction controls, so this basic example is a useful starting point for customization.
var po = org.polymaps;
var map = po.map()
.container(document.getElementById("map").appendChild(po.svg("svg")))
.zoomRange([0, 9])
.zoom(7)
.add(po.image().url("http://s3.amazonaws.com/com.modestmaps.bluemarble/{Z}-r{Y}-c{X}.jpg"))
.add(po.interact())
.add(po.compass().pan("none"));