I apologize if this has been beaten to death, but here is my situation.

I'm going to start my first SE Asia trip with a trip to Thailand in February 2012. I'm currently in New Zealand, have a U.S. passport, and do not have a tourist visa for Thailand. I'm only interested in the 30 day visa-exemption that is available on arrival in Bangkok as I plan to travel to Cambodia and Laos during my trip.

I have been hearing recent rumors of some airlines originating in Australia and New Zealand (Jetstar, Quantas, Emirates, etc...) denying boarding to individuals who do not have a Thai visa ready to show gate agents on a one-way ticket. Now, it is going to be difficult for me to get the Thai tourist visa in New Zealand because I am not near the Thai consulate, which is in Wellington and I'm on the South Island. And I really don't want/need the 60 day tourist visa.

I have proof of outward passage from SE Asia in mid-April from Singapore. However, do I need to purchase another air ticket to say Cambodia, Laos, etc.. within 30 days of entering Thailand just to show to airline staff in New Zealand so I can board the plane to Thailand?

Has anyone had any problems boarding their aircraft on a one-way ticket from Australia or New Zealand?

It depends on the airline. Most major airlines will check and deny boarding. Check if you can apply for a tourist visa by mail, a lot of consulates allow this.

If you cannot get a tourist visa, do get a ticket out of Thailand within 30 days of arrival, it can be to any neighbouring country.