Choosing your referees is an important aspect of the PhD application process. Appropriate people to provide your references would include your undergraduate tutor, director of studies or course organiser.
If it is a while since you graduated, or if you are applying for certain types of professional programmes, you should name one academic referee and one work-related referee, such as your line manager.
For reference templates and further information: http://www.ed.ac.uk/studying/postgraduate/applying/references
Further information – applying for postgraduate study at the University of Edinburgh http://www.ed.ac.uk/studying/postgraduate/applying/introduction