Brainstorm It! -- Google Traffic (and CPC) Estimator
A tool normally used by advertisers, the Google Traffic (and CPC) Estimator provides an excellent way to check the AdSense-earning potential of your "core" keywords for your Site Concept. Follow these steps...
STEP 1) Go to your MKL and do a search for your Site Concept keyword, as shown here...
This finds all keywords in your MKL that contain your Site Concept keyword.
STEP 2) Check them all and then select Export Checked (kw only) from the Select Action menu.
This puts a file called "keywords.csv" on your desktop (if not on your desktop, search your computer for a file by that name).
STEP 3) Open keywords.csv with a text editor (ex., use Notepad and then choose "File > Open" -- do not open using Excel), select all the keywords and then copy them all onto your clipboard (Ctrl-C). Open the Google Traffic (and CPC) Estimator, then paste the keywords into the text box. It should look like this (keywords in quotes)...
STEP 4) Enter $100 (USD) for the "Max CPC", leave "daily budget" and "English" at default and choose "All Countries and Territories" to complete the rest of this process. All set? Click Continue....
STEP 5) Google gives you a page of the "estimated average cost per click" ("Avg CPC") for your MKL keywords. The page will look like this...
Sort by Search Volume or Avg. CPC to better understand the data...
1) Sort by Search Volume (as in the screenshot). This yields your "bread and butter" keywords. These are the words that are searched the most at Google. The CPC is the amount an advertiser pays for a click. High-search-volume keywords tend to have "highish" CPCs, but not the highest. Why not? Because they are not usually the most highly monetizable and targeted. To see the highest CPC keywords...
2) Sort by Estimated Avg CPC (below). This gives the keywords with the highest CPCs. They will not be your largest earners overall, because most don't have high Search Volume. But the "high keywords" in this "sort" that also have "highish" Search Volume will be your biggest earners in the long run. For example...
See "anguilla villas" and "anguilla rentals" and "anguilla hotels" and "anguilla real estate" below? These words are very commercial, highly targeted (i.e., visitor is looking for a hotel) and are searched relatively frequently. These are the biggest AdSense earners at anguilla-beaches.com ("anguilla hotels" being #1)...
STEP 6) The final step?
Think... and analyze. If you have 10 or more keywords with a "Google Search Volume bar" of 
or better and with Avg. CPCs of $1 or more, you likely have a Site Concept that will be well monetized by AdSense.
In fact, though, your site will be found, as it matures, for thousands of different keywords. And your AdSense revenues will be generated by all of them, first for the easier-to-win (and cheaper) words, later for your "bread and butter."
For example, if you scroll down past the "juicy words," you will see tons of keywords with "negligible" or "zero-bar" Search Volume and "Not enough data to give estimates" for Avg. CPC. These two keywords for "anguilla"...
...are solid earners for anguilla-beaches.com. The moral of the story? As always, think about, but do not blindly obey, "the numbers."
This tool, used by Advertisers to see how much ads will cost them, is an excellent final check for your SBI! site if AdSense is going to be an important part of your monetization mix.
As long as you use your human judgement.