You can use overture free tool which is owned by Yahoo.
http://inventory.overture.com/d/sear...ry/suggestion/

another free tool from wordtracker
http://freekeywords.wordtracker.com/

Both tools will give you an overview of how many people searched for that key word. Along with related keywords and phrases to your search phrase

__________________
Niche Affiliate Marketing | I make $15,000 a month with PPC marketing and so can you!