For a short time only, 10bit software are offering their "Security 360" anti-malware software suite for free in connection with Windows 7 release. (And no, you don't need to be running Windows 7 - I'm on XP Pro, and it works fine).
Link
Check the I accept box;
put in your email addy;
fill in the captcha code, and;
click get free license button.
Install the software, then when it's running, click the button "Upgrade", which is on the right side of the product name. You will see a pop up box. Enter the e-mailed license code and click "Activate" to upgrade.
One copy per PC, normal price is US$29.95.
Deadline: 11th Nov, 2009.
I quite like the HIjack Scan feature - think built-in Trend HiJackThis (and is compatible report functions with HJT forums.

Thanks. Seems decent. I always use Spybot but this seems more powerful. Picked up one Spybot missed.

In as much as HiJackThis can also do that if you use it incorrectly, or unknowingly, yeah...

Those looking for a good free AV should go with Avast! or Microsoft Security Essentials, all the others have various issues and IObit is not known for making good security software. If you're wanting a fuller security suite, Comod Internet Security is very powerful (although at the cost of some user-friendliness).

C-net reviews give it a 4 out of 5...but what the hey, I'll give it a good testing in about a week, after a "settling in" period, just to see if there's anything majorly wrong with it...
Can't complain over-much for the price though ;)
Comodo IS is pretty good, yeah, but I've not got around to MS SE yet, so can't say anything.
I do know that one should never rely on any one product for their protection, especially if the words "Norton's" or "Symantec" are on the product ;)

So... it's free for one year only? No thanks, then. :|

avast! Home Edition
Avira Antivir Personal
AVG Anti-Virus Free Edition
Various Comodo products, including firewall and antivirus
These are some free choices, I personally use Avira. The only downside is that it pops up a huge buy-our-larger-editions box when it updates, but that doesn't bother me much. From various reports, Avira also hits more false positives than the other products but all-in-all that's a decent tradeoff for gaining more correct hits.
AVG's fee version doesn't have a scheduler worth the name - either it updates and/or scans every day (takes quite some time), or not automatically at all. It doesn't nag you do buy any other products from AVG, but the crappy scheduler makes this a no-go for me.
I did use avast!, but switched to Avira as avast apparently (back then) didn't recognise as many viruses. I don't know how the situation is today, but I assume avast has caught up at least a bit. No ads, and a good scheduler - but a potentially smaller virus database makes me go with Avira. The paid version apparently picks up traces of more malware than the free version, but since this is a comparison of the free ones, that's no argument.
I haven't used Comodo (other than their firewall, which I didn't like - that was when I began using Vista though, so I don't remember much more of it) and so cannot comment on it.

The 10bit Software program is not an AV but an Anti-Spy/Malware program. This wont replace your AV program.

Ah, that's not what the title suggested, oh well.

Fuck off spamme... oh wait its NOT one of those!
I switched to avast when I first got vista x64 and it was the only 64bit antivirus. Add to the fact its free and pretty damn good and I've not looked back.

Personally, I'll stick with Comodo. Of all the AV/firewalls I've used, it's the one that I've found suits me best.

I use Kaspersky, it's alright. But I think I'm going to ditch Kaspersky altogether in favor of my new AV software, Common Sense 2.0.

Agreed. I used it on XP as well, and I've always been happy with it. Well, except for a few false positives. Those are annoying.

No thanks, Avira user here (previously with the free suite and now with a Premium license) so I don't need anything more than that....