Well, maybe I can get this started off then. As always, everyone has different taste in software so I'm not suggesting mine is better than others, just what I like personally and use.

Firefox> I will not use IE and I feel Firefox is the best free browser out there "and I have tried a lot of them".

Ccleaner>The most handy free tool for a quick registry and junk file clean up, lite, easy to use, one of the best.

Auslogics Disk Defrag>To me, one of the fastest and very thorough free defraggers out there.

IMGburn> The one ISO burning utility that does it all, free, never had one issue with it, always fast, stable and if you go into advanced features, it may make your head spin but it has a wizard interface for those who just want basics.

PSpad> goes beyond a basic text editor and handles anything you can throw at it. Free as well.

VLC> This thing will play any video you can think of, or at least enough to please most. Even plays .ISO files etc... it has converters, video capture, video effects and much to much to discuss in this post.

Gimp> What better graphics editor for free can you ask for? Well some but that's usually because Gimp is too in depth for some. I however love the unlimited possibilities and will never use PS.

Blender3-d> The best free 3-d graphics designer you will find. A bit of learning curve there as well but it works great.

Inkscape> This is a very powerful vector graphics editor, can't ask for better for free or paid.

Tune Up utilities> As far as a thorough clean up goes, I found Tune up to be likely the best there is. While not free typically, I usually get a free version from V3.co.UK < formerly Vnunet who many times have full free versions of software. Here's the link.

Code:
http://www.v3.co.uk/downloads/
DVDfab> For backing up your dvds has a free version that is limited to one use at a time, like backup to ipod, or dvd, or whatever but is unlimited to how many times you can use it. Will back up almost any DVD.

Cole2k dvd rip pack > Another great free DVD backup suite with things like DVD shrink, etc... and while not quite as good as DVDfab for backing up the types of DVDs, it's faster and easier when you can use it.

WinRar> Excellent free archiving utility and one of the only ones I found that will take X amount of files and archive them separately instead of all in one.

Finally Picpick image capture> It's not lacking features by any means but not as robust as some, however, what it does do, is capture a lot with very easy to use interface. It's fast and free too.

There's my list for now, I could fill a forum on what I've used so these are some of my favorites. Feel free to throw in an opinion on them if you like.