Maxbert,
To be perfectly frank, the best protection "freeware" is YOU, the user.
If you take proper precautions, you don't need to install half a ton of freeware stuff that will only sit there eating up your RAM and disk space.
Two examples :
(1) Try to do your day to day work and web browsing as a standard user (NOT the Vista Administrator account with UAC enabled, I mean a real standard user with limited privileges). I can't begin to tell you how many problems you can avoid by doing this !
(2) Think twice, click once. Don't just blindly click on dialogue boxes and pop-ups ......
Also, you should INVEST in (i.e. buy, not freeware !) a good piece of defragmentation software to keep things tidy. E.g. Diskeeper which can run in the background.