Handy google map that has a ruler. Drop points on the map and it calculates a running total of the distance between them.
Rail Map Australia has a great route planner which plots routes across buses / trains and different companies. Very helpful.
Weather route planning, pretty awesome stuff... :-)
Yellow Pages provide the (currently, Jan 08) best available online mapping service for South Africa while Yahoo Maps, Google Maps, etc appear to have no street level data.