This offer appears to be instore only but my local JB HiFi currently has buy two blu ray movies, get one free. I'm not sure when the offer ends, there was no indication on any signage.
The offer applies to quite a large selection and includes some items that appear to be already quite reduced compared to other retailers. The movies range from $19.99 through to $39.99 and also some more expensive box sets.
I got Batman Begins, The Dark Knight and Shawshank Redemption for a total of $39.98.
$13.33 for a blu-ray, pretty good!
UPDATE: New link to website and confirmation of expiry:
Offer Expires Thursday 24th Dec 2009 unless otherwise specified
yeah saw this today, some titles still have last week yellow sticker sale prices on them @ $19.98ea so good deal to combine.