QANTASpower - might I suggest this website: http://gc.kls2.com/
. It will calculate great circle distance, and plot the route on a map, between any two points in the world (well, almost any two - it has difficulty of course with antipodean points). Just as an aside in case you don't know, great circle is the shortest distance between any two points on the globe - effectively what it is is if you were to take you two points, and then put an 'equator' that went right around the earth, that would be the great circle path.
Anyway, the other useful feature of that site is that it will show you what areas are 'off-limits' for ETOPS operations for the various applicable time rules. Of course, as different aircraft cruise at deifferent speeds, it isn't 100% accurate, but it gives a good idea. According to the mapper, the great circle route for SYD-LAX is doable under 180 minute ETOPS or greater. Of course, airlines don't just fly along the great circle route - prevailing winds and such are also taken into account. But again, it gives a good general idea.
Hope this is useful
"So powerful is the light of unity that it can illuminate the whole earth." - Bahá'u'lláh