Display solution/file path in the Visual Studio IDE
This is a extension available in the online gallery specifically tailored for this job. Checkout Labs > Visual Studio Extension: Customize Visual Studio Window Title.
Check out the latest release of VSCommands 2010 Lite. It introduced a feature called Friendly Solution Name where you can set it to display the solution file path (or any part of it) in Visual Studio's main window title.
More details: http://vscommands.com/releasenotes/3.6.8.0 and http://vscommands.com/releasenotes/3.6.9.0
There is not a native way to do it, but you can achieve it with a macro. The details are described here in full: How To Show Full File Path (or Anything Else) in VS 2005 Title Bar
You just have to add a little Visual Basic macro to the EvironmentEvents macro section and restart Visual Studio.
Note: The path will not show up when you first load Visual Studio, but it will whenever you change which file you are viewing. There is probably a way to fix this, but it doesn't seem like a big deal.