Read this article from Rick Glaser.

“Below is a list compiled of the top SEO, and Internet marketing tools in no particular order. Using these tools effectively can have a huge impact on search ranking, and overall traffic. Many people use different tools for different things, and good for you. This is the list that we have decided to stick by and use on a consistent basis for all of our clients. Most of the sites listed are also great resources for SEO, and Internet marketing information.

We strongly suggest checking them out and receiving updates on what they have to say. Some site may require a monthly membership, but I will personally guarantee that it will be worth every penny. SEOmoz is $80.00/mo. and the value is priceless. They offer many free tips, and high end SEO services for corporations like Microsoft. I believe they have a minimum requirement of $5,000/mo. to become a client. SEObook is operated by one of the best SEO’s reppin’ the search marketing scene, and he charges $100.00/mo. for premium membership.”