There are so many SEO tools out there to manage your site. One necessary program you must have is an analytics program that will help you drill down on what people are searching for, how often they search, where they are in the world, their click through path, whether they are unique visitors.....and much more. These programs also provide lists of keywords and keyword phrases that potential customers have used to find you. This vital piece of information helps you understand your customer and optimize your web site to maximize the number of 'eyeballs' coming to your site and thereby help you transact with them.
The analytics tool I love is StatCounter. Excellent information, easy to use and the entry level package is free.