The best tool to figure out what keywords to target accurately is Google PPC. It will take some money to do correctly but it will provide real estimates. What you do is start a PPC account using all the keywords you want to target organically. The key is making sure your ad appears every time on the first page of search results. Google has excellent tracking software and will report to you how many impressions your ad receives. If you daily budget is high enough and your maximum bid price is high enough you will appear on the first page for any keyword. If you do this for the keywords you are targeting for atleast 24 hours (most accurate is atleast 30 days) you will have a fairly accurate estimate on how many people are searching for specific keywords.
Remember Google also has tools such as Google Conversation Tracking & Google Goal tracking. You can also implement keyword phone call tracking software for your entire keyword list. Along with traffic reports, implementing these three tools when you test will allow you to accurately estimate how many new leads & sales your company would bring in if you were #1 organically in the search engines.
This way you can accurately determine what keywords will be profitable & how long until your company will see a ROI. I have did this with a company called Lee`s Landscaping & Design, Inc.. We narrowed down 900 possible keywords into 50 top performing keywords to target organically!
There is NO point being number one for a keyword that does not perform; especially when you have spent time & money to get that #1 position. If you implement the above suggestions you will always make money with search engine marketing.
For More Information:
Friendly Web Development: Keyword Discovery