Does anyone know of a tool that allows you to see historical data on keyword searches? I currently use the Yahoo Keyword Traffic Tool but that only tells you the previous month's data. Is there any way to look further back than this and any way to see more than just Yahoo's data?

Google Trends is probably going to be something that you're looking for; a lot of search terms aren't included, but the more popular ones are.

I'm not too familiar with Google Trends but it looks like that just gives you a very broad look at general terms. I'm looking for something that would be more specific. For example, something that would tell me how much the keyword "heating oil delivery milwaukee" was searched last winter.

I don't think there are any free tools out there that will give you historical information that detailed. Google Trends will give you some idea if you tweak the search, but I know it's not what you're looking for exactly.

You'll probabaly have to turn to the Hitwise service for information like that, and that can be rather expensive. Wordtracker.com will give you information for the last 24 hours, but won't give you historical information.