If you want 'real-time' on access virus scanning look into the "dazuko" module in apt/get.
That is a requirement if you want to use either clam-av or 'antivir' antivirus.
I use antivir on slackware and it works like a charm.
I presently have clam-av and I think I may change over to antivir.
Also check into chkrootkit, rkscanner, nessus too.
Also ubuntu doesn't have a firewall installed by default. It's a good idea to run one even if you have a firewall/router. You can apt/get 'firestarter' works in gnome. Also there is guarddog (needs kde) and kymyfirewall (needs kde) they're all user friendly.
@NoStop: While I agree with what you said to a certain extent , Jason didn't mention if he is dual-boot with windows sharing a fat volume, or is samba shared to other pc's at his house. So his request is possibly quite understandable, because as gnu/linux becomes more popular this may be an issue. Especially as the fstab in ubuntu doesn't stop exec on partitons in fstab by default. And if he exports home over samba to another machine, well, there you go...