LEXiT Thai Dictionary: Online Thai and English general purpose, usage, synonym-antonym and word group dictionaries.
Longdo Dictionary Service: English-Thai, Japanese-Thai, German-Thai collaborative dictionary search service.
Seasite Thailand: Multiple Thai language resources that will allow a beginner to start to learn Thai.
Thai Dictionary: Dictionary, alphabet and intonations of the Thai language.
Thai-language.com: English-speaker's resource for learning the Thai language, including a free online-dictionary with audio clips.