This was a recommendation on the Avast forum, I have just given it a run and it certainly seems good.
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PURAN (http://www.puransoftware.com/Puran-Defrag.html) <<
There are 2 versions , free and premium , the free version does all you should need.
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Puran Defrag is compatible with Windows XP/2003/Vista/2008/7 including 64Bit versions. The support for 64Bit Windows is native, so you can enjoy all benefits of your powerful processor
A good free one is MyDefrag. http://www.mydefrag.com/