I personally don't like wordtracker as their stats are quite limited. They don't have much info about lower volume keywords. I mostly use Google's keyword tool as it provides accurate enough results and it is a trustworthy source. Here are some other
free keyword research tools.
Mel is right in that you also need to take competition levels into consideration. It doesn't matter how many searches a keyword gets if you don't have the resources to get to page 1. You should also analyze the top 10 websites to see how strong they are. Ask yourself if you can build a better link profile than those websites.