first there was "e" (electronic)
(the last of the hyphen!)
then "i" (internet)
iMac (the artsy fartsy Mac users dropped the hyphen!
again setting the standard for good taste)
then with empowerment and mass approval came "u" (you)
So onward to the future as of early September 2000
Nobody wants to use "a" because that would imply one in many which simply is counteractive to all brain conditioning, er, marketing campaigns.
My prediction: the next letter is either "o" for (online), though this is a bit synonomous with "e" right now
Or perhaps "y" as the intellectuals regain control of the internet: