It's a familiar issue: you've spotted something you like in an online store, but the site won't ship to non-US addresses or charges an absolute king's ransom to do so. comGateway gives you a US address you can use, the ability to pay if the site can't process Australian credit cards, and the option to combine deliveries back to your home to cut shipping charges.
comGateway uses an address in Oregon (which doesn't charge sales tax, making it cheaper than other US locations) which registered customers can specify as their shipping address. Of course, those various options don't come for free: there's a 10% surcharge if you can't pay directly, and a $US1 per package charge if you consolidate more than three items.
The really big factor to consider is the shipping charge: a minimum of $US30.50 for the first 500 grams, and an additional $US4.10 for each half-kilo after that. For many vendors (such as Amazon for books or DVDs), that's pretty high, but it rates better than some sites.
Whether this kind of option makes sense might require careful calculation, but it's a useful option to have in reserve. For similar services, check out previously mentioned Price USA and WorldPurchases.