(1x) Arduino Uno REV 3 Radioshack #276-128
(20x) Amber Super-bright LED Indicator Radioshack #55050630
(1x) Arduino Proto Shield Radioshack #276-140
(1x) 9V Alkaline Battery Radioshack #23-866
(1x) Heavy-Duty 9V Snap Connectors Radioshack #270-324
(20x) 1/4 watt resistors (sample calculation below)
from the specs of the LEDs I used:
"Continuous forward current: 25mA"
"Forward voltage: 3V"
using the following relationship:
V(volts) = I(amps) * R(ohms)
R = V / I
we can calculate the resistance as follows:
voltage across resistor = 5V - 3V = 2V
2V / 0.025A = 80ohms
I used 100 ohm resistors so that the LEDs wouldn't be operating at their maximum ratings. Check the datasheet of the LEDs you use to calculate these values.
I've attaching a fritzing document with a breadboard and schematic view of the circuit (and included them above) for reference.