GMDesk is an application that lets you run Gmail, Google Calendar, Google Docs and Google Maps as a stand-alone application to do all your mail handling, calendar event reading etc with. No need to open it up in a web browser, or have it clutter your workspace.
Fire up GMDesk, and just alt-tab (on Windows or Linux) or Cmd-tab (on Mac) to shift between this application and the other ones you are running. GMDesk offers an easy menu as well as keyboard shortcuts to switch between different Google services, and you can specify what default service you want the application to start with. It also supports Google Apps access as well.