You can travel to the us for internal business meetings, (but will get the stink eye if it starts to add up, or if your work type is under scrutiny, like IT workers were in then 90's...and then a strong 'suggestion' to get a visa before coming back), and to negotiate a contract, like to interview / hire a US candidate, negotiate business terms, buy a firm.
You can also go as a participant in a conference for your own education / benefit. BUT not to sell goods, collect a speaker's fee, or other work.
TN is the best visa to get, and it is limited to NAFTA resident / citizens, and certain professions... but the list of professions is growing and is more than I would have thought. Definitely need a 4 year degree for the ones on the list, and not all degreed professions are included..
Also, My TN is tied to a specific employer in the US, for specific type of tasks performed (as listed on the application)....I don't know if TN's can be generated for a general use / non specific employer (for a specified type of work)...