I use Kaspersky Internet Security Suite. Just having an Anti Virus and Firewall isn't enough these days.
You also stated that you hoped Windows Firewall would have done the job. Firewalls aren't there to prevent viruses, trojans, etc. They are there to prevent unauthorised access to your computer.
If you go to a website and download a Trojan/virus by accident, then you are still telling the firewall based on your actions to allow access. Only an antivirus would help. It's also extremely important to get one that does "On Access" scanning. This saves you having to run scans all the time. As you access the file/folder it scans it before opening it. Sure it slows your computer down a little bit compared to not having it, though to be fair Norton is the worst at resource hogging, and would have been the last one I would have chosen. As I work in IT security, I would like to think I have a reasonable knowledge in this area.
The product I mentioned is good, as it has additional protection for browsers, etc. Also Kaspersky has an academy to train people to work for them. It is well know that many of their employees are ex hackers and virus/trojan creators themselves. After serving prison sentences, Kaspersky has recruited them for their expertise in defending against that form of attack.