Paul is on the right track, but allow me to elaborate. ZoneAlarm is one of the best application firewalls in existence, but I would not use it unless I had a hardware firewall in front of it. It is not an anti-hacker firewall. Any open ports are unprotected, leaving you wide open to attack.
In addition, WiFi users are particularly vulnerable. If a wireless-enabled computer within range of your router is hijacked, which is not an uncommon thing, its botmaster can make it crack your encryption and get inside your network rather easily. Even if your router has a built-in firewall, it will no longer stand between you and the bot in your network, leaving your machine(s) face to face with danger.
Use Kerio. It's user-friendly, and unlike ZoneAlarm, it will protect ports even when they're in use. To make up for ZoneAlarm's powerful HIPS, install a dedicated HIPS unit. Novatix Cyberhawk is one of the very best, and it comes in a free version. The only thing it lacks is threat removal and rootkit scanning, but it can still prevent and permanently block such threats until you take them out with a scanner.
Paul is absolutely right about viruses being the least prevalent these days. Malicious programmers rarely seek notoriety anymore, they seek to make money off your machine. Spyware is everywhere, while Trojans now make up 60% of all malicious programs. That said, Spybot is just not enough to protect you. While you can still avoid most dangerous infections with a competent firewall and a bit of discipline, you should never assume you're safe when trouble is out looking for you.
AVG Anti-Spyware and a-squared are the two best anti-Trojan products available, according to AV-Comparatives (AT-Comparatives in this case), the foremost authority dedicated to the testing of antivirus/antimalware products. Coincidentally, both of these offer free scanners, both of which I'd recommend you run once a week at least. Trojan Hunter was also a contender in the AT-Comparatives test, but they withdrew after seeing their results. While I couldn't get an actual number from Mr. Clementi, he did inform me that it was "much lower than Ewido, A-squared, and Digital Patrol," the top three.
Panda ActiveScan is a good scanner, and recently added a rootkit scanner to it. The most popular, and considered by most to be the best, is Trend Micro HouseCall. Note however, that some malware will actually block you from running Trend Micro, and I've heard that they're blocking Ewido's (AVG Anti-Spyware) online scanner as well. So it's good to have a copy of AVG Anti-Spyware on your machine at all times. And if you happen to find that Trend Micro cannot run, you can use an alternate link like this one: http://www.trendsecure.com/free_security_tools/housecall_free_scan.php#
I use System Mechanic myself, and am quite happy with it. And I don't know where I'd be without Acronis. As easy as this program makes it to backup your operating system, it is worth every last penny of the $49.99 it costs. However, if you don't need the function of backing up to DVDs, and would be content with a recovery partition on your hard drive itself (which is quicker and easier to restore from), you can register for a free copy of version 7 here: http://www.acronis.com/mag/vnu-ati7
By the way, there are two programs I know of that both contain antivirus components that will work with a conventional one, although viruses really aren't the greatest threat you have to face. These are Spyware Terminator and CyberDefender. Spyware Terminator could well be the best freeware antispyware out there right now. Windows Defender is said by TechSupportAlert.com to have a slightly higher detection rate, but I've found its resident monitor to be practically useless, and I've rarely ever seen it find anything while other products have. Spyware Terminator has much stronger real-time protection, and I have seen it find stuff. Its "auxilliary" antivirus I mentioned is Clam.
CyberDefender is a product that I'm expecting to see revolutionize the security industry. It's an all-in-one "seamless" product, integrating antivirus, antispyware, anti-spam, and anti-fraud into one contiguous unit that is supposed to "play friendly" with a conventional antivirus. But I see no need for it.
CyberDefender only came off the rogue list at Spyware Warrior a matter of months ago. In addition, they just started offering this freeware version. You will see a couple of negative reviews about it right here on CNET, but you'll see a couple positive ones as well. Mine is one of them, and it explains how the product works, if you care to look it up. I have recently replaced Windows Defender and AVG Free Antivirus with CyberDefender, and have had no need to clean up tracking cookies or anything else since. When a threat is detected, CyberDefender automatically alerts me and asks me what to do with it.