References to put depends if you are experienced or not. For people who have working experience, the best to put is:

1. Ex-colleagues
- People who know you professionally and worked with you before.

2. Ex/current employer
- This may not be a good idea to put your current employer unless you are very sure he will give you a fair comment. Best is usually some ex supervisor or someone of managerial level that will speak good of you.

For fresh graduates the appropriate references are:
1. Lecturer (preferably the one that supervises your most important project in your studies)
- Make sure you pick the lecturer you are close with and that actually knows you

2. Friends (that do projects with you)
- This shouldn't be much problem for undergraduates.

It's always to put 2 different kinds of references. The first type are people that actually evaluates your work e.g. ex-manager/ex-lecturer, and the second is people of the same level e.g. ex-colleagues/friends because sometimes employer wants to know from them what kind of character you are which manager/lecturer will not be able to tell them.

Sometimes it is best to put on your resume that "references are available upon request" so you can actually give the people you plan to put as references a call to let them know they may be expecting a call to ask about you.