Employers for Work-Life Balance
http://www.employersforwork-lifebalance.org.uk/
Cleanly designed site run by The Work Foundation that aims to help organisations implement and sustain work-life balance strategies. Plenty of excellent freely downloadable information, such as surveys, and you can also buy reports and books. It tells you how you can build a business case for work-life balance and features a handy problem solver and jargon buster.
Stressbusting
http://www.stressbusting.co.uk
Whether you're a stressed HR professional or dealing with workplace stress within your organisation, this is definitely worth a bookmark. Lots of substantial articles on issues such as presenteeism and the cost of stress at work.