The best reasons for leaving your job are those that improve your career, or make way for someone else to do the mind boggling job you put up with for all these years!
Obviously if you can get paid more money too, then thats a good reason, but you probably shouldn't say too much about that at the interview.
You got to think about your long term, so if there is some good training scheme and you can learn a new skill, that is one of the best reasons for leaving your job.
When you're in the interview, make sure you tell the interviewer how much you want to work for his/her organization because of its reputation as a great place to work.
