Websites
Biocareercenter.com and Sciencecareers.org and Naturejobs.org have hundreds or articles covering scientific training, career development, and the science job market. Many of the columns are written by career scientists.
PhDs.org provides a voice for early career scientists. It covers topics from graduate school survival to finding employment. Many of the articles are entertaining; some are cynical; most are informative.
The Career Journal is the Wall Street Journal's online career magazine for executives, managers, and professionals. Thousands of great articles on everything from writing an effective resume, to negotiating a raise.
Not specific for scientists, but very valuable advice nonetheless. Business Week has a similar online career magazine.
Career guides
Making the Right Moves: A Practical Guide to Scientific Management for Postdocs and New Faculty: This book is a collection of practical advice and experiences from seasoned biomedical investigators
Career Basics: Advice and Resources for Scientists: Seven chapters of career advice from sciencecareers.org
Career guides from American Society for Cell Biology
Career Advice for Life Scientists Part 1
Career Advice for Life Scientists Part 2
Life Sciences Research and Teaching: Strategies for the Successful Job Hunt
Career guides from the American Chemical Society (these guides have some chemistry-specific information, but most offer solid advice for all scientific disciplines)
Employment Guide for Foreign-Born Chemical Professionals
And Gladly Teach: A Resource for Chemists Considering Academic Careers
Job Search Strategies for Chemical Professionals
Interviewing Skills for Chemical Professionals