You would need to identify your requirement and the cost you can spend. There are many free tools that can be used to find the popular keywords. Google keyword tool is a great one if you wish to get all such information free of cost. This tool would skim through all the popular keyword list and give you a list of available keywords which could be of help to you. This way you can find a good keyword which would be associated with your product or service and give your business a boost. It has the keywords and phrases in more than 50 languages which is a huge exposure for beginners. However, this tool is of no use in case you need to know some long keywords of four to eight words as it cannot give results as desired.