Ethical Hacking
Edureka has provided several videos on youtube to help out beginners in all fields of technology. This video by them for ethical hacking is great for beginners. Reverse Whois lets you find domain names owned by certain people or companies. Exploit-DB is an archive of exploits for the purpose of public security.
CVEDetails provides an easy to use web interface to CVE vulnerability data. Google Hacking Database is an index of search queries which can be used to find publicly available information, intended for penetrators and seurity researchers. Find out what websites are built with using BuiltWith. Who is lets you find domain names. Way Back Machine is an internet archive of web pages.