Lonely Planet are having a Buy 3 books get the cheapest one free deal on at the moment which is applied automatically during checkout.
I also received a 30% off voucher code after I signed up for their newsletter (SUBSCRIBE30).
Also, they ship to Australia for free if your order is over AU$60.
All three of these offers work simultaneously (I've just received my books).
It doesn't say on the website or email when any of these offers will expire, so you may want to get in soon, or try your luck waiting for the latest versions to be released (check on the product page for when the next edition will be available).
nb. the 3 for 2 offer seems to have a few exclusions:
Offer available on in-stock titles only.
Offer excludes Guidebook Packs and the title Australia 42.
EDIT:
Just realised that Money Back Co has 10% for this retailer. Wish I knew that before!! :P
Pretty good!