The list of servers is outdated; my current list in line 34 of staticmap.php is:

'mapnik' => 'http://tile.openstreetmap.org/{Z}/{X}/{Y}.png',
'mapquest' => 'http://otile1.mqcdn.com/tiles/1.0.0/osm/{Z}/{X}/{Y}.png',
'cycle' => 'http://a.tile.opencyclemap.org/cycle/{Z}/{X}/{Y}.png',
'transport' => 'http://a.tile2.opencyclemap.org/transport/{Z}/{X}/{Y}.png',
'hikebike' => 'http://toolserver.org/tiles/hikebike/{Z}/{X}/{Y}.png'