I like to lay-out my palette from right to left, warm to cool. While the colors may change slightly from painting to painting the lay-out always remains the same, so that I do not have to dedicate part of my thought process to finding colors. Starting on the right (all colors are Winsor & Newton unless otherwise noted) titanium white, cadmium lemon, cad yellow, yellow ochre, cad orange, cad red, permanent magenta, transparent red ochre (Le Franc), raw umber, winsor violet, french ultramarine, cerulean blue, space blue (Le Franc), cobalt turquoise (Grumbacher), sap green (often replaced by viridian if I need a more chromatic green), ivory black. I sometimes lay out a separate worm of titanium white off to the side for pure highlights.
I have the postcards there to help me key my colors (this is a total lie, I am just a geek who really likes Mike Mignola's work)