If you are just learning about programming and not sure what you are interested in, you might want to consider a subscription to
o'reilly safari bookshelf. It gives you access to up to 10 books at a time off the o'reilly technical books online (over 3000 total) on all sorts of computer topics for about $15/month. You can read them online, print out sections, stuff like that. I used it a bunch when i was in college, i could grab a few books about whatever classes i was taking and for the price of a single book, i could have whatever i needed for the semester.
They have a few good C# books on there.
oh yeah, maybe ask your teacher?