Competent airlines flying long / medium haul into Ethiopia include:
bmi, Egyptair, Emirates, Ethiopian, Kenya Air, KLM, Lufthansa, Saudi Arabian and Turkish.
If you are travelling from Australia, you may wish to know that Ethiopian fly to/from Bangkok, Hong Kong and Johannesburg. There are no scheduled flights from Singapore or Australia to Ethiopia at present.
You might wish to look at a few airline websites, or somewhere like Travelocity / Opodo to get a better idea of prices and schedules.