The thing that's responsible for slowing down your Android phone is you. Yes, you. All those apps and junk that you downloaded over the months and years are now kludging up your phone. And once this junk is on your phone, it can be a real pain to weed it out. Here's my solution. Download and install CCleaner.

Link: This app will speed up your Android phone in seconds
via http://www.zdnet.com