Theres a huge list of high paying ones all around the internet The best paying on is on some lawyer thingy. Then there is domain registration, hosting, asbestos, etc etc.
There are a ton of free tools around, some useful for specifics, and others more useful for a general overview. As a rule of thumb though, its all common sense - think what areas of real world business have a lot to gain from their customers for example. Law and medicine are a couple of industries where they have big budgets, and are willing to pay a lot for customers/clients, because they know that on average they often get a long standing customer who ends up giving them lots of cash.
Accountants (CPAs) make a lot of gain from their clients but you can not make much from their adsense ads