They're a drier read than the book, but if you're interested specifically in the data and its analysis, there's a series of journal articles written by Piketty

They're a drier read than the book, but if you're interested specifically in the data and its analysis, there's a series of journal articles written by Piketty and another economist, Gabriel Zucman, which have more detail than the book does, "Wealth and Inheritance in the Long Run" and "Capital is Back: Wealth–Income Ratios in Rich Countries, 1700-2010". There are preprint PDFs here, along with some other papers on a similar subject by Zucman & other collaborators: http://gabriel-zucman.eu http://gabriel-zucman.eu