Apart from the stuff to the side here, my freebie essentials for Windows are:

Audacity - music editor.
Fatbits - on-screen magnifier, great for seeing details in maps.
MWSnap - screen grabber like grabzilla.
Freebie Notes - app for putting virtual sticky notes on your screen.
Xnview - a useful picture viewer.
JDirPrint - app to print out a list of what's on your drives.
MinTimer - reminds you to switch the oven off before the smoke alarm does!
Nbos Inspiration Pad - generate 40 orcs with various weapons, with a few mouse clicks.
Rainbow Folders - colour code your folders, sweep away the default yellow.
VCLZip - unzipper - and zipper.
Heatsoft Clone Cleaner - searches out duplicate files.
WinMerge - compares two versions of a document with the option to merge them.

Clone Cleaner and Winmerge make a great team if you've been untidy. HCC finds files that have the same name, then WM lets you compare them side by side, line by line if necessary, to make sure you don't delete the wrong one. My version of WM was a bit buggy though, wouldn't scroll properly, and HCC has apparently self-destructed and is now pestering me to re-download.

Some of this stuff may be available as standard in XP. I dunno, I haven't got it and don't really want it.

That mind mapper looks interesting and has a Win version, thanks.