There have been some really good tips on this thread. I agree with justamom; ThetaLove's post really covered some little details that you might not think of.
One thing that was touched upon: if you have a roommate, you still might not be safe. The rapes that happened in Philadelphia last week happened to roommates. The guy managed to squeeze through some bars that were over their window (there were only 7 inches between the bars, but he still did it) and he tied both of them up so they couldn't help each other. Sick bastard.
I hope they catch him soon and fry him.
The thing about getting a dog isn't a bad idea, either. The "center city rapist," who was just convicted of being a serial rapist in Philadelphia and Colorado, said that he wouldn't attack any woman that had a dog.
Please be smart about what you do and stay safe.