Are you a regular user of Trade Me? If you're not, then you're the odd one out, as it seems most Kiwis use the site at least occasionally. eBay is the American equivalent of Trade Me - the most obvious difference being that it's a global auction site, rather than a local one.
eBay's biggest usage come from within the United States. Don't let that put you off, though - just as Trade Me has its bargains, so does eBay. For instance you can sometimes buy an unlocked United States smartphone for half the price of an equivalent phone purchased locally. You'll find similar deals across a range of areas - but check first that the seller will ship to New Zealand and that shipping will be affordable.
Returns and warranties become difficult for goods shipped around the globe. GST may be added to goods shipped in from overseas. eBay is accessible via the web and also available as an app for Windows 8 and almost every current mobile platform.