iTunes no longer offers the option of finding duplicate songs. Fortunately, there are plenty of other ways to do so.
The Archify web service, opening to all after a private beta, records your Web navigation to your specifications and allows you to retrieve and search the records later.
AOL Computer Checkup is one of the most complete diagnostic, optimization, and cleanup tools for Windows—if you really need such a thing. At least it's not expensive ($5 a month).
Though a very good registry cleaner, PC Fix Cleaner is pricey for the actual good it will do your system.
System tweaker and optimizer Powersuite 2013 performs many optimizing tasks, and it works, but it's pricey.
In both Standard and Professional versions, Ultra Recall is a powerful, feature-rich outlining tool.
Folder Lock includes as complete a set of security tools as you'll find, and it's as secure as your passwords.
4Dots Software's handy utility is a no-nonsense tool that won't make a dent in your wallet.