In order to find the right tools to research high paying AdSense keywords, it is important to know what information you want o know about keywords. It would be just great if there were a tool that told everyone exactly what Google pays for each keyword, but that doesn't exist and anyone who creates such a tool is certain to be barred from Google forever because it is a clear violation of the terms and conditions of having an AdSense account to reveal any income information to anyone else.
You can use Adwords keyword tool to select keywords and you'll get some information. But there are many, many great tools out there that will help you select the right keywords for your AdSense campaign focus. Look for only those tools that provide information about the number of searches performed, the number of competing websites and a "guestimate" of profitability.
Keyword elite will do all of that and a lot more. Keyword elite allows you to create keyword lists with the most profitable keywords and thousands of variations. Keyword elite let's you spy on your competitors adword campaigns so you can do better.
With keyword Elite you can find the highest paying keywords for adsense publishing.
WordTracker is probably the best known and most popular tool for finding keywords that are profitable and that have little competition. However, it does entail a subscription fee so that you want to subscribe for the period that you will actually use the tool and no longer. You can subscribe for a day, a week or a month, or indefinitely. Only those people who use the tool frequently should consider an indefinite subscription due to the high cost.
NicheBot is a free tool that is really handy for this. Unlike WordTracker which costs quite a bit for a subscription, this tool has just about everything you need or want and it is absolutely free to use. It is web-based and perhaps not quite as fast as WordTracker, but it works just great. And it is being upgraded all the time with new features.
KeyWordDiscovery offers a free trial period, after which there is a subscription fee. However, it is a reasonably popular tool for keyword researching.
Overture Keyword Research Tool is another free tool that you can use. It gives you the information you need but the output is based on Overture search engines and you would do much better to get Google search engine results.
To find the right tools for you, try several of the free tools you'll find with a simple Internet search. You may find one that meets your needs very well. If not, then it is time to begin using some of the subscription services.