CCleaner

CCleaner is a free Registry and junk-clearing utility for keeping your system clean and optimized.
Pros

Basic UI: CCleaner's four main features -- Cleaner, Registry, Tools, and Options -- are clearly marked on a vertical tab menu. Initiating a scan and clean is straightforward.

Powerful: CCleaner includes most of the essentials for PC maintenance. It provides tools for clearing your temporary files, cleaning the Registry, and removing unused cookies from your browser. CCleaner also supports 64-bit systems, as well as updated support for popular applications.



Freeware: Upselling and bundling are minimal; CCleaner only offers the option to install Google Chrome, which users can easily opt out of. Compared to other free programs, CCleaner is the least ad-heavy.
Cons

Registry cleaning: If used incorrectly, CCleaner is capable of doing more harm than good. Always exercise caution when cleaning your Registry -- create a backup before starting cleanup.
Bottom Line

CCleaner is effective at removing junk files and unnecessary temporary Internet files. While using it won't dramatically improve your system performance, it's nevertheless a fine addition to your utility collection.

Publisher's Description

CCleaner is a freeware system optimization, privacy and cleaning tool. It removes unused files from your system allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. Additionally it contains a fully featured registry cleaner.
What's new in this version:
Added Windows 8.1 Update 1 and Server 2012 R2 Update 1 compatibility.
Improved Chrome cleaning: Internet History, Last Download Location and Startup item management.
Improved Opera 15 and newer cleaning: Internet History, Last Download Location and Startup item management.
Added Firefox plugin activation mode support.
Improved handling of removed and unmounted disks.
Improved Windows keyboard shortcut support.
Improved Shutdown after...


(source: http://download.cnet.com/)