When you look around your workspace what do you see? I think our workspaces should not simply be a space where we get our work done, but a tool to help support us in actually doing our work. Everyone's space is a unique extension of themselves and I would never argue that we should all have the same type of space. I do think, however, that there are a few things that should characterize every knowledge worker's workspace.

If you're a knowledge worker I think you should be able to look around your space and easily see:

The plan for what you're going to do this week.
The plan for what you're going to do today.
Your "hard landscape"
Some projects that aren't active but you want to "percolate."
And at least one thing that inspires or motivates you.

For me, this looks like:

A whiteboard that has a list of the projects I'm working on this week, any upcoming due dates, all my "hard landscape" items for this week, and a short list of "percolating" projects I want my subconscious to work on even though I'm not going to actively work on them this week.
An index card that has my daily plan written on it and it is clipped to the front of the notebook that sits on my desk.
A picture of my four younger brothers, which motivates me to work hard and be a good role model.
A meaningful quote either written on the whiteboard or written on an index card and stuck to the wall.