What is known is that big publishers typically get 50% of the
list price from retailers. This is for paper books and ebooks. This is why it has been widely reported that Amazon is loosing money on their $9.99 price for Kindle bestsellers. The 50% deal for ebooks is better than the 50% for paper books, because there are no physical returns (a cost that publishers bear for paper books).
The lowest rate seems to be about 35% to small publishers or independent authors. This is the standard rate for Amazon's DTP. Big publishers are afraid that Amazon wants to pay them 35% of list for ebooks too.
In the romance field, an author can get a 35% royalty on ebooks but no advance money. Paper royalties are much less, but you will get an advance that could end up being larger than your royalties. See
Show Me the Money! I don't think there is any other genre offering 35% to authors for ebooks, in part because direct selling to the public isn't common. I don't know what Baen books (which does sell direct) offers for example.