There are no compulsory inoculation requirements for visitors to Thailand coming from the West. Whilst not compulsory, I would recommend vaccinations for:
Hepatitis A (and possibly Hepatitis B)
Polio and Tetanus
For many people it may just be a case of checking to see if you need a booster jab. Check with your doctor or health care practitioner before you go. Some health care professionals may suggest malaria tablets and rabies inoculation. Naturally, the choice is yours, but if you are visiting the main tourist areas malaria is not an issue. If you’re planning on doing some serious jungle trekking it may be a consideration, but even then a course of tablets will be far cheaper in Thailand. The local pharmacies are invariably excellent with English speaking staff. The British pharmacy group, Boots the Chemist, has branches in places like Bangkok, Ko Samui, Chiang Mai and Pattaya.
Should you have the misfortune to be bitten by a dog or monkey, rabies vaccinations can be administered at the nearest hospital. The cost is cheap and the service good. Most tourists and visitors to Thailand won’t need to be vaccinated for Japanese encephalitis, but it may be a consideration for some people. Your doctor, local surgery or medical practitioner will be able to advise you.