This works for me:
Customers
-Client
–Correspondence {quote, letters, submissions etc… I generally don’t have too much here so 1 folder is enough
–resources
—photos
—stock photos
—supplied copy
—generated copy
—comps {illustrator, photoshop, fireworks, flash files…use descriptive names 1 folder works for me
–website
—CSS
—JS
—PDF
—Images
–Updates
—Year
----Resources
-----etc…
What I found once a system works, you tend to use it effortlessly.