My GF has just informed me that she's bought some skin whitening products "from the TV", for 3,000 baht. I tried to explain to her that they won't work and are quite likely to damage her skin and/or her general health, but she's not convinced. The fact that it's advertised/sold on TV is enough for her.

Can anyone recommend a good article/website on the uselessness and dangers of skin whitening products - preferably in Thai?

Wait till she wants this doing.

http://en.wikipedia.org/wiki/Anal_bleaching

You are fighting a losing battle if you think that a Thai lady will change her mind about whitening her skin simply by showing her the dangers either by a video or an article even written in Thai. These skin products advertised on Thai television are garbage and since there appears to be no regulatory body to investigate the claims made it's open season on the stupidity of these women. Mind you there are skin products out there that will lighten the skin but they are very very expensive and are primarily made in Japan. For a cheaper and even healthier alternative may I suggest you encourage your lady friend to take a daily 500mg. Tablet of Gluthiatone. Gluthiatone is actually a dietary supplement that aids the liver functions but one of it's side effects is to lighten the skin of Asian women. Before I allowed my Thai wife to begin taking this pill I asked my Dermatologist if it would be safe and did it work. Yes, on both counts. You can purchase Gluthiatone at GNC shops throughout Thailand. Be sure she takes it alongside a Vitamin C pill as that combination seems to produce quicker and more noticeable results.