I third Firefox and Firefox add-ons. When I first got on the 'net, I used IE. It wasn't long before my PC started slowing down and I noticed my browser history listed pages I never even visited (herbal colon cleansing, "the truth is out there", etc). Plus being a 'noob' did me no favours. My biggest mistake was clicking on a pop-up that said "Viruses have been detected on your computer. Click here to install trial software to get rid of them." Eventually it got to the point where my desktop background disappeared, I couldn't change any settings and then one day it crashed altogether. After I did a full system restore, I switched to Firefox and I haven't had any serious problems. But learning to be cautious and learning from my previous mistakes helped.
With the porn video sites, I find it's the pop-ups that cause the most trouble. I just ignore them. If they pop-up OVER the picture and block the video, just leave the site. Don't click the pop-up to close it. I did that a few months ago and it just paralyzed my laptop. Luckily, going back to an earlier restore point fixed it, but other viruses aren't that easy to deal with.
I hope I don't seem patronizing. I notice you've been on LPSG since 2004 so you've been on the internet a lot longer than I have.
I use Trend Micro which has a green/red icon indicator similar to the one bakardi420 mentioned. Although I have found the Trend Micro toolbar can be a bit temperamental sometimes.
I'd definitely recommend Firefox, it has so many good add-ons for security (and entertainment), you have to install them from the Firefox website but they're all free. And the Tools, Options... menu settings are very helpful with adjusting settings for 'cookies' and security levels, pop-up blockers, etc.
Your own caution is always good. There are SO MANY free porn sites out there that if you aren't sure about the one you're on, just leave it. There are plenty of others to choose from.