Below some tools you can use for information gathering while performing a penetration test:
IP-address: free IP Address Lookup
Netcraft: what is that site running?
SHODAN: search engine for all connected object around the world (even fridges)
Threat Agent: collect informations from open sources (seems to be down?)
Wolfram|Alpha: compute answers and provide knowledge
YouGetSignal: collection of uncomplicated, powerful network tools