NoEmotion has made a huge library of HDRI’s that they’ve created over 10 months available for free for commercial or personal use.
Just click on the links at the top that say DayHDR, EveningHDR, etc. Download links under each image. You have to pick and choose images, as there’s no one, massive file. The site is being hit by heavy downloads, so the two mirror download links are best. If not, keep checking back.