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.

Contemplating this. A few reviews on WOT says the software they provide can really fuck up a computer.

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.

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....