Google offers a new keyword tool at http://www.google.com/sktool/
This tool is pretty similar to the Adwords keyword tool, except that it includes bids, categories as well as links to Google trends and SERPS. From testing it and comparing the two tools, I would be careful when using the new sktool. I suspect this might be some beta version as the number of searches can vary widely from one tool to the other. In addition this tool suggests high bids for some keywords that do not have any advertiser.
Since it can also provide list of keywords based on your site, this is however useful to find keywords that you might have missed and which can be added right away to your account.
While I'm pretty sure that the data will become more accurate over time, to play it safe, I would use it as a complementary keyword tool for the time being.