Danny Noordzy of ax84 compiled this data for different colored LEDs conveniently on one sheet:
http://www.gothikamps.com/~danny/stuff/LED_if-vs-Ef_for-different-colours.PNG (http://www.gothikamps.com/~danny/stuff/LED_if-vs-Ef_for-different-colours.PNG)
I thought this was pretty handy, and would be useful for people playing with LED clippers, building EZ Vibes and etc...