Hipmunk has a great interface, though I'm afraid I don't always trust it to find the cheapest flights just yet. Frinstance I asked it for a flight from Sydney t

Hipmunk has a great interface, though I'm afraid I don't always trust it to find the cheapest flights just yet. Frinstance I asked it for a flight from Sydney to Melbourne on Feb 10, and the cheapest hipmunk could get me was a Virgin Blue flight for $241 -- rather expensive for this route. Checking directly on the Virgin Blue site I found fares as low as $81 on exactly the same flight. I've never had similar problems with flights with at least one end in the US though.