MasterGo
A commercial Go database program designed for searching patterns, such as when studying Fuseki and Joseki. The database contains 53059 professional games in a proprietary format (as of April 24 2011). Updates are available to all registered users.
Main site: http://www.MasterGo.com/mastergo
Demo version: http://www.mastergo.com/mastergo/downloads/mastergo_nv.exe
Distributors
The MasterGo website gives Slate and Shell as distibutor for North America and Schaak en Gowinkel het Paard and Hebsacker Verlag as distributors in Europe, but only Hebsacker Verlag mentions MasterGo in their catalog:
Direct link (in German): http://www.hebsacker-verlag.de/product_info.php?cPath=59_15&products_id=75
Reviews
I recently (08/26/11) contacted Slate and Shell and Schaak en Gowinkel het Paard. Both replied by email that they no longer carry the product.
Hebsacker Verlag does. They do not ship outside of Europe but will accept PayPal? and return an activation code. Very friendly too.