When you make your hotel or tour package bookings, remember to enquire about airport transfers. Most tour packages are inclusive of transfers to and from the Singapore Changi Airport. If these details are not in your itinerary, you may want to call your hotel and arrange for transport. Otherwise, the taxi stands at the airport are abundant and well-manned by operators who will be familiar with your transportation needs.
There are several companies that provide the airport transfer service, which you can book even before you travel to Singapore, a half or full day in advance. Among them are Limo Taxi (http://www.limomaxi.com) and Limousine Cab (http://www.limousinecab.com), best booked for groups of four and above. Surcharges apply for rides to and from the airport, starting at S$45.