Shodanhq.com is awesome.
These are fun:
http://www.shodanhq.com/search?q=X-Powered-By%3A+PHP%2F5.1.2
Many sites running old PHP from 2006. Edit as desired to find an old php target.
http://www.shodanhq.com/search?q=X-AspNet-Version%3A+1.1.4322
Incredible how many sites still use ASP .NET 1.x
http://www.shodanhq.com/search?q=%22cisco-ios%22+%22last-modified%22
Web management pages for Cisco devices that have authentication disabled.
http://www.shodanhq.com/search?q=Server%3A+Microsoft-IIS%2F5.0+
IIS 5.0
http://www.shodanhq.com/search?q=Server%3A+Apache%2F1.
Ancient versions of Apache still in use (Note: url has a dot at the end)
http://www.shodanhq.com/search?q=Server%3A+Microsoft-IIS%2F3.0
IIS 3.0 !
