My countdown timer as seen on TV: http://www.youtube.com/watch?v=Qv_ruj4lhXo

gistfile1.h

#include <Servo.h>

#define SERVO 11

byte leds[] = { 4, 5, 6, 7, 8, 9 };
#define NLEDS 6
// Manually placing the pointer since the actual labels
// ended up being slightly off.
//                     5    4   3  2   1
byte positions[] = { 148, 119, 79, 52, 27, 0 };

Servo servo;

void setup() {
  Serial.begin(9600);

  // Initialize the countdown LEDS
  for(int i = 0; i < NLEDS; i++) {
    pinMode(leds[i], OUTPUT);
    digitalWrite(leds[i], LOW);
  }

  // Point the servo at 0
  servo.attach(SERVO);

  setAndWait();
}

void setAndWait() {
  servo.write(180);
  Serial.println("hello");

  // Turn off all the lights.
  for(int i = 0; i < NLEDS; i++) {
    digitalWrite(leds[i], LOW);
  }

  // Wait for my signal
  bool readyToGo = false;
  while(!readyToGo) {
    byte b = Serial.read();
    switch(b) {
    case 'g': // GO!
      readyToGo = true;
      break;
    case 's': // Synchronize
      Serial.println("s");
      // blink a sync pattern
      for(int i = 0; i < NLEDS; i++) {
        digitalWrite(leds[i], HIGH);
        delay(10);
        digitalWrite(leds[i], LOW);
      }
      break;
    default:
      delay(50);
    }
  }

  for(int i = 0; i<NLEDS; i++) {
    digitalWrite(leds[i], HIGH);
    servo.write(positions[i]);
    delay(1000);
    digitalWrite(leds[i], LOW);
  }
}

void blinkErratically() {
  // Select a random light to blink.
  int led = leds[random(0, NLEDS)];

  digitalWrite(led, HIGH);
  delay(random(20, 100));
  digitalWrite(led, LOW);
  delay(random(20, 100));
}

void loop() {
  // If the control channel sends an 'r' command, reset state.
  // This allows testing and stuff.
  if (Serial.available() && Serial.read() == 'r') {
    setAndWait();
  }
  blinkErratically();
}

sync.py

#!/usr/bin/env python

# worse is better

import os
import sys
import time
import serial

def timeTilNearest(secondFactor):
    t = int(time.time())
    nearest = 10
    nextT = (int(t / secondFactor) * secondFactor) + secondFactor
    duration = nextT - t
    return duration

def sync(ser):
    print "Sending sync cmd..."
    ser.write("s")
    ser.flush()

    print "Waiting for sync response."
    b = ser.readline().strip()
    print "Read", repr(b)
    assert(b == 's')


if __name__ == '__main__':
    ser = serial.Serial("/dev/tty.usbserial-A900acmg")

    print ser.readline().strip()

    sync(ser)

    t = time.time()
    duration = timeTilNearest(3600)
    # duration = timeTilNearest(30)
    nextT = t + duration

    while t < nextT - 10:
        # Compute the time on each iteration.
        then = nextT - t - 10
        duration = min(15, then)
        print "It's now %s, flashing in %ds at %s" % (time.ctime(t),
                                                      then, time.ctime(nextT))
        if nextT - t < 600:
            sync(ser)
        time.sleep(max(0, duration))
        t = time.time()

    t = time.time()
    print "Counting down at %s (%f to go)" % (time.ctime(t), nextT - t)

    for w in (10, 9, 8, 7):
        # Do a vocal countdown.  I recalculate the time duration on
        # each request so I don't have to worry about how long it
        # takes to issue the say command.
        duration = nextT - w - time.time()
        print "Sleeping at %d for %f" % (w, duration)
        time.sleep(max(0, duration))
        os.system("say %d" % w)

    print "Adjusting volume and stuff at %s." % (time.ctime(time.time()))
    os.system("""osascript -e 'tell application "iTunes" to pause'""")
    os.system("""osascript -e 'tell application "iTunes" to set sound volume to 100' &""")

    os.system("say 6")
    time.sleep(max(0, nextT - time.time() - 5))

    print "Executing at %s" % time.ctime(time.time())
    ser.write("g\n")
    ser.flush()

    time.sleep(1)
    print "Playing music"
    os.system("""osascript -e 'tell application "iTunes" to play track named "Auld Lang Syne"'""")

    # How long to do the light show.
    time.sleep(108)

    print "Sending an r"
    ser.write("r\n")
    ser.flush()
    time.sleep(1)