Enthusiasm

Personally, I have always found that my level of interest in and attention to a subject is directly proportional to the teacher's enthusiasm.  To me this seems logical.  If a teacher is passionate and enthusiastic about the subject he/she is teaching, then the student has a reason to be excited also.  Similarly, if the teacher can't be bothered to take an interest in what he/she is teaching, why should the student?
Throughout my educational experience people have asked the eternally boring question: What is your favorite subject in school? The answer can go one of two ways: (1) whichever subject in which the student feels most capable; or (2) whichever subject is taught by the coolest teacher.  I always picked number two.  In seventh grade my favorite subject was English, in eighth grade - Math, in ninth - French.  It changed and was almost entirely dependent on who the teacher was and how much they enjoyed their subject. 
The best example of this was my seventh grade English teacher who absolutely loved Shakespeare.  We spent a great deal of time in class discussing Shakespeare, learning about his life, and reading his plays and poems.  In most situations this would have seemed a major overkill but because the teacher was so committed and sincere in her teaching, it seemed perfectly natural. 
While passion and enthusiasm are clearly an important part of teaching, it is also important that the passion be in the subject area of the class. I once had a history teacher who was incredibly passionate... about Lunchables.  She was convinced that they were the spawn of Satan and that all the children would rot in hell forever for eating Lunchables on a regular basis.  Most of the kids in that class couldn't tell you when the Magna Carta was signed (which by the way was 1215 [lunchtime!]) but we sure learned a lot about processed meat.
Go Lunchables!