The overwhelming majority of those were from government or scholarly, peer-reviewed sources. xkcd is probably the most exhaustive web-comic I know in terms of

The overwhelming majority of those were from government or scholarly, peer-reviewed sources. xkcd is probably the most exhaustive web-comic I know in terms of social commentary. Humor of some of the points aside, it's a valuable visual comparison, seeing how many resources could be acquired with a small fraction of the current United States debt.