Avast (Free Antivirus)
The (free) registration that Avast asks for every six months has confused people before, so I keep that in mind when choosing which of these excellent programs to use.
General cleaning of temp/excess files
2gb free backup. It’s what I use. I’ve heard people say good things about Dropbox, but since I know this system, I like it. It is also cross platform (and can sync), so if you have a work Mac or *nix system, you’re almost certainly covered.
I’ve had so many damn problems with non-standard drivers that it’s not funny. Use this to back them up to a CD to avoid having to scour the web when you reinstall your OS.
Best defragger in my experience. Especially with Vista, but also XP.
Ever have a window offscreen and you can’t grab it back? This helps. An absolute MUST for netbooks.
Uninstalls all of a program, including crap left in the registry. You want the free version.
K9 Web Protection
If you have kids and want a netnanny, I use this one, largely because it’s so customizable from *my* end, so *I* choose what gets through and what doesn’t. You can also allow temporary access.
I love the desktops at Simple Desktops.
What’s your favorite freeware to put on a clean install?