Definitely get AVG free. it freakin owns everything else.
For a firewall, I highly recommend ZoneAlarm Free edition, but make sure you just get the free, the "full" version is totally not worth it at all. Also, if you have Windows 7, they don't have a version of the free firewall out for it yet just FYI.
For a browser, to be honest, if you are using IE8, you will be fine. I personally like Firefox better because of the addons, but IE8 is at least as secure though it is a little slower. Pretty much all the old security issues with IE are no longer valid with IE8. MS did a really fantastic job with the security in it and they release almost weekly security updates. Google Chrome is also secure and lightning fast but it has some rendering issues.
Opera and Safari are also secure though I personally don't like them (especially Safari...), but the latest versions of FF, IE, Chrome, Opera, and Safari are all secure within reason.
Not trying to be a fanboy. Of course, it's hard when you own the best console eve... dang it
