To make any material shadeless in Cycles you simply need to use an emission shader with a strength of 1.0. You can plug textures and anything you want, but the final shader (connected to the output) needs to be the emission shader.
The fun part of shadeless is that you don’t really need light rays bouncing around. If you’re creating an entirely shadeless scene (like a 2D animation) you can set all light path settings to 1 and the samples as low as 20. Less samples won’t give you less quality but you will start seeing aliasing. Though it might be useful if you’re going for a 8‑bit look.
For even more performance you can render with the GPU and set the tile size to the entire render size.