CCleaner is good as most of the other answers will suggest.
site report.
http://www.siteadvisor.com/sites/piriform.com?premium=true&client_uid=3286841423&client_ver=3.0.1.163&client_type=IEPlugin&suite=true&aff_id=0&locale=en_us&os_ver=6.0.2.0&ref=safesearch
They do a defrager as well but would recommend this instead http://mydefrag.com/
Just don't do the iobit.com.
Adaware, spyware or viruses 5
phishing or other scams 23
Bad shopping experience 1
Rating: Phishing or other scams
alfranatic is the latest sock puppet account being used by IObit to try and hide the "red" reviews from being read by users of siteadvisor. Such behaviour is unacceptable and this site needs to be turned RED. Why would a genuine reviewer spam the review page with 4 "green" reviews in a row unless to try and hide the red reviews which are slightly below it. Shameful tactics!
This company is involved in an ongoing dispute regarding the theft of the malware database more than one other security company. iobit.com have given no credible evidence to refute the claims and have tried to cover up their theft, unsuccessfully, from the online community. Iobit.com is also engaged in the unsavoury practise of using black-hat SEO using porn keywords and other explicit terms in order to trick unsuspecting users into downloading their "products" (search google for iobit.com+porn games to confirm, they tried to remove the page after being exposed). They have also registered a number of "fake" reviews on siteadvisor.com and mywot.com supporting their products in the face of overwhelming public disgust at their actions. Most of the green reviews on this page are fakes.
You can read the allegations here: http://malwarebytes.besttechie.net/2009/11/02/iobit-steals-malwarebytes-intellectual-property/
And more here:
http://news.softpedia.com/news/Malwarebytes-Accuses-IObit-Plays-Dead-126389.shtml
Based on my own careful analysis of the evidence presented by Malwarebytes, I give this site a RED rating and urge SiteAdvisor to protect their users by also rating this site red. The spamming of the comments page by the site owner (and their sock puppet accounts) does them no favours.
PS just thought you should know as i only post green downloads in my answers and if they are green i check.