Wordtracker -FREE keyword suggestion tool，返回人们最近搜索的关键词。

网址：http://freekeywords.wordtracker.com/

做英文seo必备工具

还有这两个个google keyword tool也不错

https://adwords.google.com/select/KeywordToolExternal

https://adwords.google.com/select/TrafficEstimatorSandbox