According to Openflights I've got (in descending order of # of flights):
Virgin Australia (inc Virgin Blue and Pacific Blue), Delta,
Etihad Airways, United Airlines, Singapore Airlines, Jetstar Australia, Qantas/Qantalink, Air New Zealand, Regional Express, Air Canada, Thai Airways, Cathay Pacific, South African Airways, Aerolineas Argentinas, LAN Airlines, Lufthansa, Air France, Swiss International Air Lines, Scandinavian Airlines System, Finnair, Virgin America, AirTran, Hawaiian Airlines, TAP Portugal, Alitalia, Germanwings, Air Berlin, Virgin Atlantic, Southwest Airlines, Dragonair, GOL, Oceanair, Sharp Airlines. (33)
In addition from memory:
Ansett, Impulse, Kendell, Aeropelican, KLM, Malaysia Airlines, Air China, US Airways, Kenya Airways, Kingfisher, Air India, Avianca Brazil, TAA/ Australia Airlines, Emirates, Easyjet, Jetstar Asia, British Airways, Aer Lingus, Skywest (when independent)
That comes to 52.
I'm surprised it's so many to be honest.