I would maybe buy Crystal Ball, because that is actually pretty cool.
I would also put in my vote for Crystal Ball. I haven't needed it at school - and don't know if I will next year - but have used it in my internship for the summer and really like it.
Probably 95% of what you do in school will be within Office. For the other bit, you're better off waiting to know what software your school/class will use. First, you get a discount while at school, and second - at least for some of the stats software we've used - some of the datasets we needed for class were in the format of the program the professor recommended for the course.