Nobody has mentioned McAfee. I used to have Norton, but as previously stated, it was a huge resource hog. So I got rid of that and my IP offers McAfee for free, so I'm using that now. Any opinions on it's effectiveness?
It's effective. Of course, Norton is effective too if you have the right product for your needs and keep the definitions up to date (critical with any product). McAfee can eat up CPU cycles in a hurry though, but that's somewhat of a requirement. The more popular an anti-virus program is the more viruses and malware are designed to circumvent them, requiring the antivirus software to be more thorough (which can eat cpu cycles). Good protection does not come free (and I'm not talking money).
There's no harm in trying McAfee. It's much, much better than using nothing at all.
I use Microsoft Security Essentials, but I'm not sure I'd recommend it to the average user. It is not the most comprehensive security product available, but it's much better than nothing.