Win 7 does an excellent job of optimizing, not like you had with XP and Vista.
Windows defragmenter works fine. You don't need another one.
As previously mentioned, CCleaner is an excellent program from cleaning up after yourself. The registry cleaner portion thereof works perfectly.
If you have a great fear of using the registry cleaner which many of the contributors here use, namely, the CCleaner registry cleaner, then let Microsoft clean the registry for you. That's a new thing with Microsoft.
Go to this location and you will be amazed. MS Windows Live OneCare safety scanner: Free online tool for PC health and safety