vBPress is a WordPress plugin by forgueam and pjhile that seamlessly integrates WordPress with vBulletin.
vBulletin (vB) is a commercial Internet forum software, now with community social network features produced by Jelsoft Enterprises and vBulletin Solutions, both subsidiaries of Internet Brands. It is written in PHP and uses a MySQL database server.
Download and info: http://wordpress.org/extend/plugins/vbpress/