Exploit-db like websites, where people can search for security bugs

[johhny_at_poland77]

If someone has to decide between 2 very similar server programs, or operating systems, then it searches on sites like: 

http://www.exploit-db.com/search/

so that there he could get enough information about the given program/os's historical security bugs.

Do you know exploit-db like sites, where can people search for security bugs? What's the best place to search? What's the best place to compare two softwares/os-es?

Thank you!