I've been using Norton for years, without any problems. The system I bought last July came with Norton Internet Security, which has a firewall as well as the AV, and it also helps with adware/spyware. I'm not too sure of the effectiveness of the firewall, although it has stopped some applications from accessing the internet all on their own.
I always recommend Spybot and AdAware to anyone who asks for my help with their computers. I've been using them for years as well, and I've been quite pleased. I'm not a high-risk surfer but every once in a while they'll find something. Just make sure you update them at least once a week. I Have Norton run a scan once a week automatically, and I run manual scans on Spybot and AdAware once a week as well. Spybot also has some nice administrative tools which can help with start-up programs and some registry problems. If your comfortable with computers, switch it to advanced mode. No extra charge!
Something else to look at is http://www.grc.com/default.htm. They have numerous small programs which you can dowload for added security. They also have an online test called ShieldsUP! which tests your defenses against hackers. I've used it without any problem.