If you mean silence the ringer, check out Foxyring. It allows you to silence the ringer during hours of your choosing. You can also set a list of privileged phone numbers that can always get through. It has the ability to turn off the ringer, or just change ringer volume based on geographic location, though I haven't tried that myself.
My favorite thing is actually a widget that comes with the app that allows you to quickly turn off your ringer for a given time period (up to five hours) and have it turn back on at the end of that time so that your alarm (for instance) works the next morning.
I use Setting Profiles to shut everything off between the hours of 11pm and 6:30am, but that doesn't actually shut off the phone itself. Slight correction: I turn off everything except the ringer (I don't have a landline so in the event of an emergency, I still want my phone ringing), but the GPS, notification sounds, calendar reminders, etc are all off.
It also will handle other things (such as location based settings like turning on my wireless when I'm home or at work)....similar to Locale.
I know that's not exactly what you're looking for though if you want the actual phone to turn completely off then turn itself back on in the morning.