I use Mireth's NetShred, which is available in both Mac and Windows versions, and ShredIt. The former seems to create extra hard disk space by getting rid of JUNK - and as I no longer store my credit card details (after being cybermugged of $500 a couple of years ago) I always use it whenever I have used ebay or bought goods online to delete my financial details from the computer.
The ShredIt is particularly useful for using on rewritable CD-ROMs when you are sending out confidential data (by courier/recorded delivery, obviously) to erase the old data before reusing the disk. I was told I had to use this sort of software by the Information Commissioner's office, when I used to be a Charity Secretary - who also told me my laptop data MUST be encrypted or I'd be committing a criminal offence - Civil Service and MOD PLEASE NOTE!!! :evil:
ccleaner.. (free) cleans up all old programs and applications , removes cookies and registeries
speedItup.. (free) does what it says! speeds up computer and internet connections.
10bit smart defrag. (free) the newer version also optimises too!
most of these can be googled for. but beware that most are not free,, you need to hunt for the free ones!!!!!
also have as a extra Veoh TV.. its like media player but better in as you can save and download fav films and tv prgrams.. works very well with www.watch-films.net all the latest films and lots of our fav oldies.