As you may remember, Google announced they are replacing the external keyword tool with the Google Keyword Planner tool.
Well, it took some time, but now the legacy external keyword tool is gone. If you try to access it at adwords.google.com/select/KeywordToolExternal you will see an error page that reads:
Keyword Planner has replaced Keyword Tool
With Keyword Planner, we've combined the functionality of Keyword Tool and Traffic Estimator to make it easier to plan search campaigns. That's why Keyword Tool is no longer available. You can use Keyword Planner to find new keyword and ad group ideas, get performance estimates for them to find the bid and budget that are right for you, and then add them to your campaigns. We've also added several new features with Keyword Planner.
So now to get any keyword data similar to the external keyword tool, you need to login to your AdWords account. If you do not have an AdWords account, you will need to sign up for one to get this data.
The keyword tool is one of the oldest and most useful tools from Google. Seeing it go is pretty historic.
Forum discussion at WebmasterWorld.