Here are a few links to a variety of travel advice for all visitors. 

Helsinki City-Airport Bus

This service is offered by Finnair ("Finnair City Bus") and travels back and forth every half-hour between the airport and the Central Railway Station. The bus company can be reached at 0307 23746. The driver accepts credit cards on board. As of Dec 2013, the fare is 6.30 Euros.

From the Railway Station, the bus runs from 05:00 am to 00:00 midnight, and stops at the Hotel Crowne Plaza on the way. Total travel time between the railway station and the airport is 35 mins.

From the airport, the bus runs from 05:45 am to 01:10 am and stops at any number of hotels, depending on where the passengers are going. The travel time from the airport is therefore longer than the travel time back to the airport.

A timetable in pdf format is available at  Click on "View the schedule" under "Finnair City Bus".