Google's added a new Traffic Estimator tool that lets you discover traffic for a term without having to actually add the term to an account or campaign. You can see clicks per day, average CPC, cost per day and average estimated position.
The tool's gotten a good reception in our forums so far. But folks still want more features. Fortunately AdWordsRep, Google's official rep for AdWords on our forums, has been busy answering questions and gathering up the suggestions. So jump in if you've got feedback to share in this thread: New Adwords Traffic Estimator.