What a great thread. I love free tools. Many that is listed here I have been using for a very long time but I thought I would add a couple to the list. So here they are:
Speedtest by Ookla
http://beta.speedtest.netTest your system throughly
http://www.tweaking.comThere is a free version and a paid version. The free version is not crippled so if you don't need the pro version you still get enough to do a lot of repair to a system. The forum is a great place to get answers to problems that might come up. The man who runs the site is very knowledgable.
http://www.grc.com home of Spinrite the very best hard drive repair/test you will find on the internet. He also offers some really great free tools that are very powerful so be sure to read about them totally before using them. They can mess your system up if not used properly. Mr. Gibson is a very well known computer wizkid who is in my book an absolute genius.
So there you have it 3 of my favorite tools. I do use a lot more but so I will list them on my website and come back with a link. Till then have a great day.
mobear420