Finding a Volunteer Opportunity in Thailand
If you don't want to move permanently to Thailand, one of the easiest ways to see the country and also be productive on your visit is to volunteer.
Even though you will not be earning wages, you do still need a work permit to volunteer in Thailand, according to the website for the Thai Embassy in the United Kingdom. If you have an arrangement to volunteer for an NGO (charitable non-governmental organization), ask them to write you a letter that you can use to obtain your work permit.
When you start looking for a volunteer position that suits your skills and interests, you will find there is no shortage of need. Organizations like Thai-Experience.org, which offers "volunteer vacations, gap year abroad programs and community service projects in Thailand" can match you with a volunteer gig. Work could include teaching at an orphanage, helping villagers to develop and market their handicrafts, and fundraising for the Thai Experience organization.
Consult the Travel Channel's website for a list of eco-volunteering opportunities. This could include volunteering for the Wildlife Friends of Thailand, which runs all sorts of smaller centers and offers the chance to help some of the cutest monkeys, dolphins, and elephants on the planet.
Another major issue in Thailand is human trafficking, where young women from rural areas are coerced into going to the cities, primarily Bangkok and Chiang Mai (the two biggest cities in Thailand), and working in the sex trade. If you want to help provide counseling, education, and resources to these women, sign on with Kaya Volunteer, a reputable volunteering organization whose slogan is "responsible travel."
Keep in mind, however, that with Kaya or most other volunteering organizations that recruit foreigners, you will have to pay a fee in order to volunteer. This should include your food and housing, as well as the costs of training you for your job duties, and some portion of your payment will probably go to the cause that you are volunteering in support of. However, if you contact an NGO independently while you are in Thailand, you may be able to do similarly useful work and get out of paying the fee that these tourist-oriented companies charge.
An extensive list of NGOs in Thailand, both Thai-owned and foreign organizations like Goodwill and UNICEF, is available here. Hopefully, you will be able to contribute where you are most needed and have an unforgettable travel experience while you are at it.