From Nathan Bransford's blog (7 March 2011):

Let's look at a back-of-a-napkin breakdown of a print book vs. an e-book (all numbers approximate):

$24.99 hardcover:
$12.50 to the bookstore (roughly 50% retail price) - [me: so half of the amount we pay goes to the freaking bookstore, not the actual, you know, CREATOR, of the stories? Shocking.]
$2.50 to $3.75 to the author (between 10-15% of the retail price)
$1.50 for paper, shipping, distribution (again, approximately. UPDATE this would be for a high-print-run book, HarperStudio cited $2.00 as average)
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Around $8.00 to the publisher, which is split between overhead (rent, paying editors, copyeditors, etc.), marketing, other costs, and hopefully some profit assuming enough copies are sold.

$9.99 e-book (agency model):
$3.00 to the bookseller (30% of the retail price)
$1.75 to the author (25% of the publisher's share)
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Around $5.24 to the publisher, split between overhead, other costs, and hopefully some profit