If you want something to carry to class the smaller the laptop the better. I stated out using a 14" Compaq laptop for college but after 3 months I ended up replacing it with a 10" netbook which I have used for the past two years without any problems. Needless to say I have been much happier with the 10" system since it's not a pain to carry around.
The Alienware M11x is particularity good because in addition to offering good performance and being tiny it also has great battery life. A couple of other good options are the HP Envy 14 and the Asus U30JC.
The gpu in the Asus is on the weaker end of the spectrum however it has great battery life while the HP has a much faster gpu but also has much shorter battery life.
I'm using my 13" MacBook from school and I think this might be the best size for me to get or possibly a little smaller. The thing about the M11x though, is the price.
h ttp://www.shopping.hp.com/webapp/shopping/computer_can_series.do?storeName=computer_store&category=notebooks&a1=Category&v1=ENVY&series_name=ENVY14_series&jumpid=in_R329_prodexp/hhoslp/psg/notebooks/ENVY/ENVY14_series&aoid=35252
That's odd. As far as I can tell that is a direct link to the HP official site. If you search Google for "Envy 14" without the quotes the first result should be the right place though.