How do you estimate the online demand strength for a market?

in Google, Yahoo, and MSN

[Macbeth]

How does one do this and what tools are available?

Is there a way of getting trended searches by month for the past 12 months when trying to which markets are on the increase?

[andye]

One way is to set an an account with the PPC search providers (Google Adwords, Overture) and use their traffic estimation tools.

A.