We know about the various radio station roving team giveaways but you generally you have to be lucky to hear/be near them at the time but here are two from Channel Nine that you can look up beforehand to see if they will be close to you:
Muffin Break Today Jeeps (SYD, MEL & BRIS)
http://today.ninemsn.com.au/article.aspx?id=181101
(Locations updated each Monday morning for the week ahead. If the location is near a Muffin Break you get fresh muffins too!)
GO! Garnier Jeep Locations (Over summer 09/10 - VIC, NSW, QLD)
http://www.facebook.com/note.php?note_id=361032140190
(Locations updated each week. City and country/beach areas covered).
They have had plenty of stock to giveway in my neighbourhood visits so you don't have to be one of the first ten or so people… ;-)
(Not sure if this qualified as a freebie post for the main section so putting it here.)