Ideally, you are pulling keywords from multiple sources - from traditional search engines, metacrawlers, contextual campaigns, and any other keyword development tool and resource you can find.

If you are familiar with keyword creation and management, you can skip to the tools listed below, or view the free tools page for useful software and links to help you build your keyword databases.

The most critical component to keyword management is your ability to track a conversion, action, or goal to a keyword. Maybe your goal is to generate a large amount of traffic, and the conversion "event" is not important to you. Online brand awareness is. That's a noble goal, however you're missing the point of direct response online advertising if your goals are as simple as "to increase traffic" or "to grow the business". Online advertising begs to be measured, so don't leave your campaign out in the cold.

Maybe your campaigns are more sophisticated, and your goals encompass a hybrid model in which traffic from top level, one or two word keyword sets deliver the bulk of your traffic, but don't contribute much in the way of direct conversions. If you're tracking your campaigns correctly, with a 30 day (or longer) cookie, you will find that these terms influence your more specific, higher converting keyword sets. If you do it right, this leads to more impressions for those higher value terms.

The best tools for the job are listed below. Remember to keep your keyword lists organized, and continually test new keyword sets.

RapidKeyword	A very useful tool. The way the software splits keyword lists and pulls fresh keywords out of Wordtracker is very inituitive. ** 24 hour free trial - $69.99 **
Dowser	New tool, fresh to market. Not a lot of experience with it. Email me if you have comments.
NicheBot	NicheBOT offers free keyword research services, innovative web site software, search engine ranking tools, and more.
Adwords Analyzer	This is a very popular program for keyword development. Similar to Rapid Keyword; you can view the # of competitive searches by keyword, split and combine lists, and it pulls data from multiple search databases. AA also gives you a way to strip the annoying bullet points and numbers from Overture Search Tool results.
Google's Keyword Sandbox	Google's tool for drilling down into Google's search queries. It's a great tool for finding related keywords, but not as good at drilling down to more targeted but less searched phrases. Overture's tool and Wordtracker are better for that.
Keyword Density Values	Good lord we have know idea what this is but it's very scientific and geeked out beyond belief so we couldn't resist.