As you sip your afternoon pick-me-up, consider Steven Heller's take  on the humble Solo Traveler, aka the coffee lid. It's ubiquitous, it's barely noticeable, it's... Freudian?
The Solo Traveler lid is a substitute for a mother's breast--what we might call nature's original travel lid. The flat covers with the tear-back openings offer no such metaphoric representation. Instead, spout = nipple. Paper cup = warm skin. Coffee, tea or soy = mother's milk. Ergo the lid is a nurturing apparatus.
The product design of the coffee industry has gotten more and more high-tech: there's the Clover , the hand-held espresso-maker , this wacky 88-drops-per-minute iced coffee maker ... Not even my trusty Chemex is safe ! But in the midst of that caffeinated hoopla, one item has remained, if not entirely unchanged, than at least unswayed by snobbery and science.
In an article on the lid from 1996, Phil Patton  estimates we use about a billion and a half lids every year--but that number's sure to have grown in the past decade. The first plastic, snap-on lids were invented in the '80s (before that, they were cardboard). MoMA's design curator Paola Antonelli suggests in her "Design for the Real World" piece  on Studio 360 (scroll down) that this is due to advances in plastics manufacturing at the time. Soon enough, all the modern details emerged: fold-back spouts, caf/decaf indicator buttons, and all those "Caution! Hot!" warnings. Heller and Antonelli's favorite, Jack Clements's Solo Traveler , was designed for ergonomics--note the handy lip cut-out--but it turned out it also worked perfectly for foamy drinks he could never have predicted when Clements patented the Traveler in 1986. There are other highlights: the Dart "Lift-n-Lock," with it's central steam chimney (way more nipple-like than the Solo); or McDonald's old-style lid with Braille lettering and little stamped arches logo, which they've sadly discontinued . They're meant for mobility, sure, but they look pretty good framed on the wall.