The scroll bar on that site is a cool way to represent the saturation. Scrolling with the mouse wheel changes saturation on http://colourco.de/ too, but it’s more obvious on the hailpixel site that you can use the mouse wheel.

Do either of these "intelligently" pick colors? Just playing around with them, it seems I can't make anything ugly.

I prefer this site. clearer and simpler, focus, than http://colourco.de/

Sort of, but providing the scheme progressions is really neat.

any idea how this guy calculated the colour for the text dynamically so as to maintain the contrast difference?