Hi. I am an Australian. I am currently travelling in south korea and will be going to Thailand to work as an volunteerEnglish Teacher for 1 month in August/September and then i would like to travel around until 30 November when i fly home to australia. Australians do not need a visa for a 30 day stay. But i would like to stay longer. Can i get a tourist visa for my whole stay or should i arrive in thailand and stay for 30 days then get a visa??? Or when i arrive at the airport get a visa there???????????????

A tourist visa is valid for 60 days and can be extended for 30 day upon payment of 1900 baht/filling out form and presenting photo. This visa must be obtained at a Royal Thai Consulate outside of Thailand. It can not be obtained at the airport.

Work in Thailand requires a work permit and a non immigrant visa so be sure what you are planning is ok with authorities.

You still need a visa for a 30 day stay, it's just that a visa-on-arrival can be obtained at the airport whereas a visa for a longer stay (2 months) can only be obtained from the consulate. Make sure you take your return tickets, passport photos and money when you go to the consulate, and allow at least a couple of days for them to process it. Check the opening times too - Sydneys consulate only handles visa applications between 2pm and 3pm, Dublins only works on a postal system and can take up to 3 weeks, Amsterdam stamps them as you wait.

I would go to the consulate and apply for a 2 month tourist visa, that way you are covered for most eventualities. I'm not sure whether volunteer work (unpaid) counts as an infringement of a tourist visa?

it's just that a visa-on-arrival can be obtained at the airport

This is a common misunderstanding; as a person from Oz can not obtain a visa on arrival. What she would get at the airport is a permission to stay for 30 days stamp, but this is not a visa and she does not need a visa for a 30 day stay.

There is a "visa on arrival" available to a few countries that do not have Thai consulates available to them. See MFA Visa Page for a good breakdown.