What's the best replacement anti-virus software for Norton on Windows Vista?

AVG I have been using it at home work and school. It has worked great for me. Yes also it is free.

If you have an AOL screenname (free sign-up), you can download the AOL-branded McAfee Virus Scan Plus for free here: http://safety.aol.com/isc/BasicSecurity/
Don’t worry, it won’t install any other AOL software on your machine. It says “special edition,” but I’ve tested it and as far as I can tell it is the full version of McAfee VirusScan Plus. It includes the virus protection as well as a firewall and spyware scanning.

You already are familiar with AVG, so I won’t mention that again.

ALWIL software offers a free version of its avast! antivirus software for home users here: http://www.avast.com/eng/avast_4_home.html
I have not tried avast! myself, so I can’t recommend or non-recommend it, but C|Net’s Download.com Editors gave it 5 stars while users gave it about 4 1/2. Read their reviews here: http://www.download.com/Avast-Home-Edition/3000–2239_4–10019223.html

There’s also Comodo’s AntiVirus 2 which is free: http://antivirus.comodo.com/
Download.com readers only gave this product 3 out of 5 stars however: http://www.download.com/Comodo-AntiVirus/3000–2239_4–10538177.html

Clam Win is an open-source antivirus program: http://www.clamwin.com/
It does not include a real-time scanner however. You need to conduct all scans manually.

Finally, you can get ZoneAlarm Internet Security Suite free through TrialPay by going here: http://www.zonealarm.com/store/content/company/products/znalm/freeDownload.jsp
Basically how it works is if you agree to complete and offer from on of TrialPay’s advertisers (Netflix, eMusic, etc), they you get the software for free. I got 75 songs from eMusic for 99¢ and then canceled my membership in order to complete an offer. You just have to remember to cancel before you get charged (I canceled my eMusic membership the same day I signed up for it after downloading the free music). I wouldn’t recommend this TrialPay approach to everyone, but it does work if you follow the rules.

Hope this helps!

clamwin all the way
http://www.clamwin.com/

In my considered and professional opinion, the best replacement anti-virus software for Norton on a Vista machine is to back up any useful data, reformat the hard drives, removing all traces of Vista, and then install a preferable operating system. :-)

I’d go with AVG as well.