When your writing a reply below the "To:" box next to the formating buttons is a link "« Plain Text" click it and it should just send plain text emails. At least thats been my understanding.
On the web, yes.. however on the GMail app for the Google phone, I can't find the option and in fact now I'm pretty sure it doesn't exist at all.. So yet again forced to hit my PC to mail you guys...
Could we do this the lazy way and enable HTML emails on the list ha ha.. why out of interest are they disabled anyway?..