People who allow Google to place ads on their site are naturally looking for the keywords that pay the most money.  If you know how adsense works, you may have noticed that to make money
with adsense you need not only to target a large number of users.
Another important side of the equation is to have customers that will
click on ads that pay more.

The concept of keyword cost is defined by the Google Adwords program.
Each advertiser creates ads linked to the words that they think are
more related to their businees. They will give the price they consider
to be the most adequate. In this process, the words that drive most
consumers will become more expensive. Thus, different words have
different costs per click.

If you are an adwords customer (which
you should be), you will see the costs of some words that you are
trying to target. However, in general is not so straightforward to know
what is the price payed by a word.

After searching this topic, the phrase "mesothelioma lawyers" comes up on the top of the list and I had to find out what mesothelioma meant. Apparently there is a lot of money in asbestos litigation and law firms are willing to pay big bucks for anyone who searches on this very specialized term. Since very few people have ever heard of the term "mesothelioma" its a relatively safe bet that anyone who searches on that term or who is willing to click on the term is someone with a high probability that they can make money off of.

Here are two categories of top dollar keywords:

Law

Health Care

These terms are sure to change over time, but this will give you a good starting point.