You might think of it largely as a web site, but eBay claims to make a sale via one of its mobile applications every 15 seconds. Its newly updated Android application has now been made available for Australian users.
The eBay app does pretty much what you'd expect -- search listings, set up alerts, track your own auction activity, and pay for goods via PayPal. As you'd expected on an Android application, it also supports voice search. Like the main eBay site, it focuses on Australian search results if you're logged in with an Australian ID.
eBay is a free application, available via the Android market.