Don't listen to people who say you need Ultegra. I have Tiagra/105 on my bike. So far it survived couple of crashes and me using it. Also one thing to keep in mind is that you are commuting to school. So I'm guessing you will be leaving a bike outside. Then you definetly might want something that is not flashy, with 32 spoke solid build wheels. I have 01 (I think before they went to compact frames), Specialized. Since I got it only thing I had to replace was a front chain ring. It was bent curtosy of some driver. Do you have hills in your area? If there are no major hills or they are relatively short I would recommend a single speed bike. Less things that can go wrong, and needs to be adjusted.
Also visit commuting forum, there are lots of people there that will have great recommendations too.