Adding more Mapbox tilesets Tutorial
MapBox layer provides some baselayers, but you can add additional Mapbox layers (or Tilesets) into Openlayers yourself.
Once you installed MapBox and the OpenLayers modules, you may be asking "What's next ?" because there is no MapBox layer provided out-of-box. This page will help you to add MapBox layers (a.k.a "Tileset") into OpenLayers in Drupal 6.
In Drupal 7 some MapBox tilesets are provided but more can be added following this tutorial.
Then back in your Drupal installation
admin/build/openlayers/layers/add for Drupal 6.MapBox layer provides some baselayers, but you can add additional Mapbox layers (or Tilesets) into Openlayers yourself.