The following airlines serve Singapore Changi SIN Airport.
Airline Terminal
Air Canada, AC Terminal 2
Air Canada, AC Terminal 3
Air China International, CA Terminal 1
Air France, AF Terminal 1
Air India, AI Terminal 1
Air Mauritius, MK Terminal 1
Airasia, AK Terminal 1
Alitalia, AZ Terminal 1
American Airlines, AA Terminal 1
ANA, NH Terminal 2
Asiana Airlines, OZ Terminal 1
Austrian, OS Terminal 1
Bangkok Airways, PG Terminal 1
Bestair, BST Terminal 1
British Airways, BA Terminal 1
Cathay Pacific Airways, CX Terminal 1
China Airlines, CI Terminal 1
Continental Airlines, CO Terminal 1
Delta Air Lines, DL Terminal 1
DHL Air Limited, D0 Terminal 1
Egyptair, MS Terminal 2
Egyptair, MS Terminal 3
Emirates, EK Terminal 1
Etihad Airways, EY Terminal 2
EVA Air, BR Terminal 1
Iberia, IB Terminal 1
JAL, JL Terminal 1
Jet Airways (India), 9W Terminal 3
Jetstar Airways, JQ Terminal 1
Jetstar Asia, 3K Terminal 1
KLM, KL Terminal 1
Korean Air Lines, KE Terminal 1
LOT - Polish Airlines, LO Terminal 2
LOT - Polish Airlines, LO Terminal 3
Lufthansa, LH Terminal 2
Malaysia Airline, MH Terminal 2
Northwest Airlines, NW Terminal 1
Qantas Airways, QF Terminal 1
Qatar Airways, QR Terminal 3
Royal Brunei Airlines, BI Terminal 2
SAS, SK Terminal 1
Saudia, SV Terminal 1
Silkair, MI Terminal 2
Singapore Airlines, SQ Terminal 3
Singapore Airlines, SQ Terminal 2
South African Airways, SA Terminal 2
South African Airways, SA Terminal 3
SWISS, LX Terminal 1
TAP-Air Portugal, TP Terminal 1
Thai Airways International, TG Terminal 1
Tiger Airways, TR Terminal B
TNT Airways, 3V Terminal F
Transaero Airlines, UN Terminal 1
Turkish Airlines, TK Terminal 1
United Airlines, UA Terminal 3
US Airways, US Terminal 2
US Airways, US Terminal 3
Valuair, VF Terminal 1
Virgin Atlantic Airways, VS Terminal 2
Virgin Atlantic Airways, VS Terminal 3

More details on airlines from the Singapore Changi Airport website.