The best freeware, and the one I use most would be
SPM, Statistical Parametric Mapping, a very advanced software for analysis of brain images.
http://www.fil.ion.ucl.ac.uk/spm/
Other than that, I also use HBA (human brain atlas), MRicro, PVeout, Autoroi, Braintools, Skullstripper and other software developed by different brain imaging labs worldwide. The nice thing with software development in the academic world is that it's almost always free to use since the idea is that everybody gain from sharing knowledge and using the same or similar, analysis tools.
Ok, this is very uninteresting for all of you since you have absolutely no use for software which makes neat little compartments of images of brain volumes, so I will also mention some other software I use a lot:
Total Commander
Eudora Light
Firefox
Opera
Adobe acrobat reader
Winamp
Quicktime
Realplayer
IrfanView
Miranda
"There are in fact two things, science and opinion; the former begets knowledge, the latter ignorance." - Hippocrates
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