Plain language on-line resources

General sites

The US government plain language site 
Garbl's Writing Resources 
The US government usability site

On-line training

The National Institutes of Health training course (US)
Plain Train (Canada)

Guidelines

Federal Plain Language Guidelines (US)
Drafting Legal Documents (Office of the Federal Register US)
Securities and Exchange Commission Plain English Handbook (US)
Making Regulations Readable (Office of the Federal Register US)