Yuri Arcurs, the famous Microstock photographer, has developed a useful tool to help find the right keywords for stock images. The Photo Keywording Tool is available for a long while, but only recently I found the tool and started to use it.
The tool is simple to use and effective.It makes tagging / keywording – one of the necessary (but less fun) steps in Microstock photography less painful.

In a nut shell, this is how it works:

• Type several keywords.
• List of relevant images from Shutterstock (or Crestock) will appear.
  Choose images similar to yours.
• List of keywords from the chosen images will be created.
• You can add / remove keywords from the list and use it.