Meet the LEDs

Form Factors (size, shape, type)

Bulb

3mm 5mm

RGB

RGB is really 3 lights in one.

Common anode vs. common cathode: http://flashgamer.com/arduino/comments/rgb-led-common-cathode-or-common-anode

If you are mixing colors, diffused LEDs might be better otherwise you can see the individual diodes lit.

Pixel

BlinkM

Ghetto Pixel http://www.instructables.com/id/Ghetto-Pixels-Building-an-open-source-BlinkM/#commentactioncontainer_CF0Q2CTGP7IS5IH

Strip

Array / Matrix

7 segment

High Power

SMT

Properties

Operating Properties

Forward Voltage
Forward Current

Light properties

Luminosity / Luminous Intensity / Brightness
Wavelength
Viewing Angle

Hackable Consumer Products

GE light strings
IKEA Dioder

Product Page: http://www.ikea.com/us/en/catalog/products/20119418/ Tutorials:

http://marco-difeo.de/2012/03/28/irdioder-ikea-dioder-hack-mit-atmel-und-infrarotempfanger/