I have put together a list of the 3 airline alliances, and their primary members. This information is particularly useful when you are deciding which frequent flyer program to transfer your Starwood points to.

Star Alliance:
Air Canada
Air New Zealand
ANA
Asiana
Austrian
BMI
Lot Polish Airlines
Lufthansa
SAS Scandinavian Airlines
Singapore Airlines
South African Airways
Spannair
SWISS
TAP Portugal
THAI
United Airlines
US Airways

Oneworld:
American Airlines
British Airways
Cathay Pacific
Finnair
Iberia
JAL-Japan Airlines
Lan
Malev
Qantas
Royal Jordanian

SkyTeam:
Aeroflot
AeroMexico
Air France/KLM
Alitalia
Continental Airlines
Czech Airlines
Delta Airlines
Korean Air
Northwest Airlines