The Kura-Kura tourist bus has a route linking Seminyak with Umalas in the north and Kuta in the south, however it runs infrequently.
Metered taxis are easily hailed. A trip from the airport with the airport taxi cartel costs about 150,000Rp; a regular taxi to the airport, about 100,000Rp. You can beat the traffic, save the ozone and have a good stroll by walking along the beach; Legian is only about 15 minutes away. Blue Bird has the most reliable service.