Non-immigrant visas are issued to allow a foreign national to come to the U.S. for a short period of time for a specific purpose. If you are travelling to attend a conference or convention, you may be able to apply for a B-1 business visitor visa.
In general, speakers from foreign countries are not allowed, by U.S. law, to be paid for their services.
Here's relevant information from the State Department pertaining to international speakers:
No salary or income from a U.S. based company/entity, other than expenses incidental to the visit. If honorarium will be received, activities can last no longer than nine days at any single institution or organization; payment must be offered by an institution or organization described in INA 212(q); honorarium is for services conducted for the benefit of the institution or entity; and visa applicant will not have accepted such payment or expenses from more than five institutions or organizations over the last six months.
Full details can be found here:
Business Visa Purpose Listings
SpeakerMatch caters almost exclusively to both meeting planners and speakers in the United States.