Keyword inventory tools such as the free ones at Google and on Overture or the paid ones such as Wordtracker are not the only sources of inspiration for your SEO content. Two great places to find keywords are in your web logs and email.
One of the best source of article topics that are naturally search engine optimized are reflected in the phrases that your customer use when they ask questions about you as an expert or about your products or services? What sort of posts do they leave on your blog or chat forum? Examining this material may give you more targeted keywords and key phrases then a SEO keyword tool ever might!
Also the great thing of finding these search engine friendly key phrases on your site already means that you don't have to rewrite content to suit the search engines. There is no harm in giving this novel approach to finding keywords for your pay per click advertisements and other forms of online promotion.
Another way to find keyword search phrases for you site would be to do some very specific targeted research by sending out a questionnaire to the people your customer mailing list to see what they would like to see in terms of content or information on your web site. You can then take their response and wrap them into keyword phrases. Chances are there are many potential customers out there phrasing their searches in the same way as the respondents to your market research. If your customers are the lethargic type you might have to offer some kind of prize to get their attention so they will fill out the questionnaire.
Once you find the targeted keywords by searching through all of the material on your website and in your email that could qualify as customer generated market research you are all set!