Sloppy content management will likely lead to sloppy results. I learned a great folder structure system from Kurtis Beavers when I was working at the IU School of Journalism. He picked up this 4-folder structure while at Finelight. It’s great for web and print production; other structures are better for websites and action script Flash.

Above is a photo of my workflow for a magazine I am coordinating and redesigning.
Keep one folders for each individual project and remember to save multiple versions!
ART
Store photos, screen shots, linked graphics and other images.
INFO
Store documents of text/copy, research, guidelines, styleguides and possibly a copy of your freelance contracts.
LAYOUT
Use This folder for working documents like Photoshop, Flash, Illustrator and Indesign.
FINAL (PDF, JPG, SWF, ETC)
Documents that can be submit or shared. This is handy for reviewing multiple versions.
Other Structures
Developing a Sensible Folder Structure
Folder Structure and Project Organization Best Practices
Project folder structure for a web designer