Symantec Antivirus 10 Corporate Edition found many trojans and other software on my comp which norton internet security 2005 didnt find :S odd for the same company.
Antivir Personal Edition v7
it's fast, effective, and it's free
it also has heuristics
on their site, you can download a new heuristics engine for it.
it is more aggressive than the previous one, though it's currently a beta, and I've read that sometimes it might recognise a program as a virus when it isn't.
though I've never had that happen.