Possible to independently use Macbook Pro and external monitor?
I have not seen this.  Two things I have tried that help me, however, are:
Pin windows that you want on the side monitor to all spaces
I've often treated my second monitor as more a static workspace that doesn't change no matter what space I'm in.  You can do this by
System Preferences --&gt; Expose and Spaces --&gt; Spaces --&gt;
Click &quot;+&quot; under Application Assignments, and add the applications you want to stay on the second monitor to &quot;Every Space&quot;.
Run a virtual machine in the second window
Using VMWare I sometimes run Windows or Lion on the second monitor in full screen.  Add that virtual machine to &quot;Every Space&quot; as described above, and then within that machine I can use spaces and have it run independently of the primary workspace.
Neither method gives you exactly what you want, but they provide a few other options you might try that will still give your working style a boost.