What is the lowest latency communication method between a computer and a microcontroller?

Question

I have a project in which I need to have the lowest latency possible (in the 1-100 microseconds range at best) for a communication between a computer (Windows + Linux + MacOSX)

Answer 1

Ethernet

Look for a board that has a gigabit ethernet port directly connected to the microcontroller, and connect it to the PC directly with a crossover cable.