If you have ever been developing a VisualForce page for salesforce.com and received an internal server error, there may be a quick work around. I hit this problem a few days ago and spent hours trying to figure out what was going wrong in my code. There were no errors in the Developer Console and it appeared that my code was completing successfully. Well, as it turns out, it wasn't failing inside my code, there was something else going wrong on the server side.
I still don't know exactly what I was doing to cause the error, but it seems that the error was related to the Development Mode editor for VisualForce. I disabled the "Show View State in Development Mode" setting (if you're looking for it, its on the user settings page in setup go to Setup > My Personal Information > Personal Information). After disabling the view state setting, the error went away and my page is rendering correctly.