Lots of companies/projects work in the field of information visualization, on the bookshelves of almost all of them, you can find Tufte's books. He's largely considered the leader in the theory of displaying information in as dense and as clear of a method as possible than enables people to perceive the encoded information as rapidly and as correctly as possible.
He's best known for sparklines we all enjoy when looking at tables of stock prices, but those are likely the the least of his contributions to the field.
references:
http://www.palantirtech.com/
http://www.futurepointsystems.com/
http://www.caida.org/tools/visualization/walrus/
http://en.wikipedia.org/wiki/Visualization_(computer_graphic...
http://www.esri.com/
http://nvac.pnl.gov/