What you need depends largely upon how important it is that the data on your PC doesn't fall into the wrong hands. If you use it for banking etc, or there is sensitive info on it, then it's very important.
Other things to take into account might involve a situation where you've lost all the family photos/documents because something has wiped them out, but hasn't actually stolen your CC password.
An answer for the former is to have very good system immunity and prevention capabilities.
A good answer for the second case (and good practice generally) is to make backups of anything you don't want to lose.
Malware has moved a bit from being a vandalistic hobby for geeks to being a multi million dollar business, with gangs involved, purchasing trojan horses etc to order from dodgy software writers. Some of the most successful of these are those that quietly run in the background without wreaking havoc, so you're less likely to notice them. This category includes rootkits, which can be quite difficult to detect and remove.
Not wishing to be alarmist, here, most of us will never happen across one of these, but it can happen. A lot of the M$ patches that are released are for discovered vulnerabilities, usually in browsers, but really for anything that can be exploited.
Suggestions for prevention/system hardening: Make sure your computer and all its applications is fully patched and up to date.
Secunia is a good online check for this.
Consider using a
hosts file which will prevent the browser loading known dodgy sites.
There aren't many resident free antispywares around. Windows Defender is one.
SPywareTerminator is another, and better. (Get the smaller download, without the toolbar.) (Unless you want the toolbar.)
SpywareBlaster you already have. Excellent.
Tighten up the security settings on your browser. Don't have it configured to run scripts/activex without you getting the option to block same. Consider a better browser than the integrated-into-the-OS IE series. Firefox is good. Get some extensions for it like Noscript, and Ad-block. Opera is another popular one.
Consider running from a user account rather than an admin account when on the internet. I find this too limiting. There's a program available called "Drop my rights" which allows you to run a browser or email application, not as an admin.
Use a two way software firewall. I use Comodo, but have herd/read that ZA is considered OK.
Consider disabling services Windows runs by default that often aren't needed for the average user. Not only can this improve security, it soups up the PC.
Here's a useful tweak site.
Any folders you have that contain sensitive data, encrypt or password protect them.
For scanning and cleaning I use (and never find anything more fearsome than a cookie) the aforementioned SpywareTerminator,
Superantispyware, AVG AS, Asquared (link above) and Spybot.
For rootkit detection
AVG Antirootkit is easy to use...a lot of them really aren't, unless you're an expert.
AdAware will never be on my computer again. The 2007 version is resource hungry and buggy, the forum next to useless, support for the old SE version is about to cease. (How long since you've updated it?)
If you want to get really techy, virtualisation and sandbox programs, and HIPS might be the way to go. Not for the average user, though.
This all just touches on applications/procedures to use. All links have free versions. Sorry to rabbit on.
Or you could get a Mac. No challenge in that, though!