More monitors are more productive. Larger screens (only if good resolution, etc.) are also more productive. All monitors should typically be within peripheral vision, otherwise notifications coming up might not be noticed.
If you are looking at a macbook/macbook pro - also consider glossy vs. matte screen (glare can be an issue).
Finally, if you're really trying to be productive, consider other visual and audible distractions, flow interruptions, taking breaks during work to increase mental stamina, length of time spent at work.
Consider a real keyboard and mouse. Consider synergy: http://synergy2.sourceforge.net/
If you are looking at a macbook/macbook pro - also consider glossy vs. matte screen (glare can be an issue).
Finally, if you're really trying to be productive, consider other visual and audible distractions, flow interruptions, taking breaks during work to increase mental stamina, length of time spent at work.