I know J.R. has made some earlier posts about the electoral college system; in particular, how unlikely it is that it will ever be eliminated by amendment to the Constitution.
I was reading an article last week that Maryland and New Jersey have enacted laws that will allocate their electors to the winner of the national popular vote, if enough other states also enact the same law to equal a winning margin in the electoral college (270 electoral votes). Some other states have partially passed the law (e.g. legislature passed it but governor didn't sign).
I'm not sure if the backers of this law will ever be able to get enough states to enact to reach 270 electoral votes, but it is definitely more of a possibility than getting 3/4 of the states to ratify a constitutional amendment.
I know the framers of our Constitution did not intend for the President to be elected by national popular vote, but I believe the current implementation of the electoral college is not done as per the Constituion. I believe there is nothing in the Constitution requiring states to even hold elections for President, just that the states can allocate their electors as they see fit. (I could be wrong on this, but I think I'm basically correct). Since the 19th century most states have allocated all of their electors to the winner of their statewide election.
Therefore, to me it seems that the individual states can change the way they allocate their electors, and if they want to do it by national popular vote, they can do it. The good people of Wyoming would lose their 4 to 1 voting power over the good people of California, but that's too bad!