A red 5 volt LED where the resistor is built right into the plastic. No more messy current limiting resistors!
We've often found ourselves in need of an LED for breadboard prototyping but hate that the current limiting resistor takes up so much space. To solve this we went on the hunt for an LED that already had a resistor built in and voila! We found this!
Luminous Intensity: 5 mcd
Wavelength/Color Temperature: 635 nm
Viewing Angle: 60 deg
Forward Current: 20 mA
LED Size: T-1
Lens Shape: Dome
Mounting Style: Through Hole
Here's a video showing off the current limiting abilities of the LED, and miserable failure of LEDs that don't posess that feature.