Recently I added a few new links to the downloads page but have not mentioned it here. I have opened up the parts inventories for all sets on Rebrickable for anyone to download for free use for any purpose.
The files are updated monthly so are not meant for up to the minute data. If you want that, the API has allowed real time and full inventory access for a while now. What they will allow is some great analysis of the data and hopefully some interesting insights into the trends.
I only stipulate one condition for using this data: Play Well!