Mercury is such a dense liquid that cannonballs float in it. Humans float on it too (you'll have to scroll down a bit for the picture), but it's probably not a good idea. If you just can't resist hopping in the mercury vat, elemental mercury is less likely to kill you than mercury compounds. It used to be sold as a laxative (officially branded Dr. Rush's Bilious Pills but colloquially known as "thunder clappers"); Lewis and Clark's campsites can sometimes be identified by the mercury they deposited along the way.
What would be the density of Asteroid B-612? (That's the home of the Little Prince. [full text]) Randall Munroe describes life there. [more inside]
Population 7 Billion By 2045 global population is projected to reach nine billion. Can the planet take the strain?
UnitConversion.org is quite the resource to easily convert between different units of measurement. It has over 2100 units in 78 categories, which range from those that are common, such as, length, weight, volume, currency, velocity, and pressure, to more specialized categories like magnetic flux density, electrostatic capacitance, and surface tension.
Back To The Future, Hill Valley is a "from the ground up" conversion of the videogame Grand Theft Auto: Vice City, with the goal being to re-set the game in the world of Doc Brown, Marty McFly & Biff Tannen. Sample videos of the progress so far. Please note that Hoverboards don't work on water. Via.
2 4 8 16 32 64... Storybytes, an ordered archive of nanofiction. It's been done before, by syllables (17), by the masters (Classic Short Stories), and by comedians (Book-a-Minute). But in a dense natural language, with a high meaning-per-word, perhaps bytes would value infodensity more objectively: 256b, 1k, 4Kb. But then again, isn't a spec as much of a cop out as a rigged dictionary? Perhaps the highest infodensities are achieved by works which will have no human readers.