It kind of fluctuates, but I can almost never go to bed before midnight unless I have to wake up REALLY early.
I went through a period for 6-9 months where I consistently went to bed from 2:30-4 AM (this was around the time of my first semester of college and freshmen winter break). It was horrible, and I got out of the habit.
Now, I go to bed at 1-2 AM, and I'm happy with my schedule. I wake up at 9-10 AM.