Auslogic's Registry Cleaner is always free and beats the heck out of CCleaner. Also their Disk Cleanup is great, particularly if you want to get rid of all those Windows update rollback directories (as if you'd ever uninstall a critical update).
Both the Disk Cleaner and Regisrty Cleaners are about the best in the business, both agressive yet completely safe.
They also have a decent Regisrty defragger if you really feel the need to gain a percent or two reduction in the size of your registry and the disk defragger is decent although I've yet to find a disk defragger better than Norton's Speed Disk circa 2003.
I did a substantial study of comparable system utility packages available for free trial at CNET. I must have downloaded and used at least 50 different packages and even though you can get a number of the funtions provided in BoostSpeed for free and often of decent quality (CCleaner is pretty good and the price is right) in the end I decided to spring for the $49.95 and buy the entire package.
I've been using it for a couple months now and am very happy with it.
It would have been nice to get it for free but I have no issue shelling out the cash for something that's worth it and in my opinion BoostSpeed is indeed worth it.