Today I was wondering about the phrase "spic and span," so instead of asking Jonathon, I looked it up myself. I feel so proud of myself.
Anyway, apparently it comes from a very old phrase (around 1570), "spick-and-span new," where "spick" means "spike" or "nail," and "span" was a wood chip or splinter produced in making something out of wood. It referred particularly to new ships, where the "spans" produced in the making of the ship were still pale-colored and bright, rather than that darker gray they get soon afterward, and the nails were all shiny and new.