Looking for the most profitable keywords is never easy, and you will find its almost impossible to guess what is going to be the most profitable keyword in any niche.
Having the best tools to help you with this is absolutely key to your success, remember research is everything in this game!
The good news is the best keyword research tools are actually free.
I personally use two tools very often (every time I create a post or article - even this one)
Worktracker keywords : http://freekeywords.wordtracker.com
Wordtracker was created to show what people are searching for on the web. There are free and paid for versions of the service, the paid* for version gives you lots more detail. It is worth the money but if you do not think you can afford it at this time the free version is a very good tool.
The free version gives you an estimated number of daily searches for any keyword, very usful information and I have found the estimates to be pretty solid which is very important to know when you are selecting long tails for your site.
Googles external keyword tool: https://adwords.google.com/select/KeywordToolExternal
The google keyword tool has arguably got the most up to date information as it is powered by the top search engine. This is not my favorite part of the google tool though. I really like the keyword ideas it gives you, It offers up keywords I know I would never have thought up on my own.
If you are looking into keywords for ppc then this tool gives you some vital information on the advertiser competition. There are other tools that you can look at for more detailed information on the advertiser competition but the competition bar gives you good information while you are going through the initial stage of looking at all keyword possibilities.
Please post any comments or question you might have.
To your success,
David and Ashley
* http://www.wordtracker.com/order.html
UPDATE
I have just found out about another keyword research tool http://labs.wordtracker.com/keyword-questions/ - I have not had much of a chance to put it to the test yet as I only found out about it today, but from what I have seen it is a great tool.