Bing-ip2hosts (o.4) by Andrew Horton is useful for web intelligence and attack surface mapping of vhosts during penetration tests. Find hostnames that share an IP address with your target which can be a hostname or an IP address. This makes use of Microsoft Bing.com ability to search by IP address, e.g. "IP:188.8.131.52".
Download and read more about Bing-IP2hosts here - http://www.morningstarsecurity.com/research/bing-ip2hosts