American Airlines and United / Continental are the main US carriers but DELTA and other airlines fly as well. The main Latin American Carriers are LAN, TACA. Iberia has daily flights from Madrid. KLM flies to Quito and Guayaquil as well.
Most flights arrive late in the afternoon or in the evening. You will most definitely need to spend a night in Quito or Guayaquil before flying to the Galapagos Islands the next day.
Flights to the Galapagos depart from Quito or Guayaquil. There are two main airports in the Galapagos Islands, one in Baltra (serves Puerto Ayora in Santa Cruz Island) and one in San Cristobal. There are many flights a day. TAME, AeroGal and LAN are the main carriers. Flights to the Galapagos take about two hours, our Tip Top Travel Lufthansa City Center agency in Quito can arrange flights for you.
The way out process is very similar. You will need to fly from the Galapagos (usually before 12pm) and have a transfer – hotel night in Quito or Guayaquil to take an early flight out the next day. If you can book an international flight leaving after 7pm you might be able to save that night in the mainland.