I got an email last month from the National Mental Health Association asking if I'd help raise awareness of mental health in the workplace. A link to their website can be found here - Welcome to the 2006 May Is Mental Health Month Campaign!
I've also selected a number of quick links to specific work-related guidance:
Depression Checklist: Know the Signs
Mind Your Stress: Tips for Managing Stress on the Job
Workplace Activity Ideas
Intervention Strategies for Employers: What to Do When You Think an Employee May Need Mental Health Help
Finding Your Balance: At Work and Home