Anti-virus
1. Avira Antivir PE - http://www.free-av.com/
2. AVG antivirus - free.grisoft.com
3. BitDefender - http://www.bitdefender.com/
Spyware
1. Adware - http://www.lavasoftusa.com/
2. Spybot - www.safer-networking.org/en/index.html
3. Spyware Blaster - www.javacoolsoftware.com/spywareblaster.html
4. Spyware Terminator - http://www.spywareterminator.com/
5. ewido - www.ewido.net/en
6. Superantispyware - http://www.superantispyware.com/
Firewall
1. Comodo
Office software
1. OpenOffice - http://www.openoffice.org/
2. NeoOffice - http://www.neooffice.org/
Image software
1. Gimp - http://www.gimp.org/
Browser
1. Firefox - http://www.firefox.com/
Media Player
1. VLC - http://www.videolan.org/
Others
1. Money Manager Ex - sourceforge.net/projects/moneymanagerex
2. CD BurnerXP Pro - www.cdburnerxp.se
additonal info.
http://tech.yahoo.com/qa/20080121161837AAyxtfc
http://www.osalt.com/ - comprehensive directory of open source alternatives to commercial software.