WINDOWS UPDATES
Automatic
Every day at 5:00 PM
ANTIVIRUS
Avira AntiVir Personal Edition
Avast!
Microsoft Security Essentials
Panda Cloud Antivirus
FIREWALLS
Outpost Security Suite Free
Online Armor Personal Firewall
ZoneAlarm Free Firewall
You can go
HERE for a very good guide setting up a firewall
Browsers
Firefox or Chrome
Add Ons
LastPass or KeePass
Web of Trust (WOT)
SpywareBlaster - This excellent product will protect both Internet Explorer and Firefox.
Spybot S&D Immunize - Adds a large list of malicious websites to Internet Explorer's Restricted Sites list just as SpywareBlaster does. This can be found by clicking the Immunize button on the left side of SpybotS&D.
You can add a layer of protection to your home network or computer by using OpenDNS
or Norton DNS
Norton DNS uses Symantecs exhaustive Safe Web database
Sandboxie was already mentioned but you need a analyzer to analyze the files you download before recovering them
Buster Sandbox Analyzer
http://www.wilderssecurity.com/showthread.php?t=259357
Create a limited users account
Buy a lifelong liscence of malware bytes pro. Its only around $25 thats it.