Here's a list of some budget-friendly security tools you can use for prevention if you need new security tools or if you're looking for an alternative to replace something you're already using (it's not necessary to run two anti-virus products).
Microsoft Baseline Security Analyzer (http://technet.microsoft.com/en-us/security/cc184924.aspx) Great tool to confirm that your computer settings align with security best practices
SecuniaPSI (http://secunia.com/vulnerability_scanning/personal/) Powerful software to find security holes in your software before the bad guys do
ShieldsUp (https://www.grc.com/x/ne.dll?bh0bkyd2) A handy website to identify firewall configuration problems that can leave you exposed on the internet
Avira (http://www.free-av.com/) Award winning antivirus program for people without a security budget
Spybot Search and Destroy (http://www.safer-networking.org/en/index.html) Award winning program to detect and remove spyware that antivirus often fails to detect
Spamfighter (http://www.spamfighter.com/) A highly effective tool to catch spam before it catches you
KeePass (http://keepass.info/) A simple and extremely secure tool to both organize and protect your passwords