Be Careful Using AdWords for Keyword Research
There are a few ways to address this challenge:
If you have the budget, my top recommendation is to buy a few, very broad keywords in AdWords, send them to a relevant landing page on your site, but realize you probably will lose money on the campaign. The goal isn't conversions, but rather to learn by watching the keyword terms/phrases for which you get impressions. This is also great conversion-testing if you have the budget to invest, but even a week or two of data can be highly valuable for future keyword targeting.
When searching in AdWords, start broad, and then enter narrower queries and note the new phrases that come up. Make sure to use exact match, and be diligent in testing variations. Google only lies through omission.
The relative numbers of searches aren't perfect (as you can see above), but they are relatively decent. In fact, I'd say they've improved in what they show vs. the actuals you'll see compared to prior years. However,
Use your own analytics as a guide to find new terms/phrases you might be imperfectly targeting. And if you see keyword variations that have a unique or different intent, it might even pay to create a more targeted page for that query, and you often need less work to rank, since Google uses the "indented results" system to drop a second URL from the same domain directly underneath the first one on a given page.
Now I'd love to hear from you - what are your experiences around keyword research in AdWords? Are you seeing the same thing we are? You can share your thoughts in the comments and/or use the poll below (from a new service called Quipol that has some fun twists):