Security and related tools

IPsec-Tools (win)
http://vpn.ebootis.de/ (os)

Adware
Ad-Aware (free)
http://www.lavasoft.de/software/adaware/

Spybot (free)
http://www.safer-networking.org/

Anti-Virus
AVG (free)
http://free.grisoft.com/

Avira AntiVir (free)
http://www.free-av.com/

Personal Firewalls
Sygate (discontinued, plz google!) (free)

Ashampoo (free, reg.req.)
http://www2.ashampoo.com/webcache/html/1/product_1_0050__.htm

Outpost (discontinued)

Anti-Spy
XP-AntiSpy (free)
http://www.xp-antispy.org/

XPy (os)
http://sourceforge.net/projects/xpy/