There is no real easy answer to this particular question. It's easier to talk about to someone else than to the angry person. My advice is simple, but hopefully effective.

The first thing you would need to do, is do your research! Before approaching the subject you will to find out about local anger management courses that would be both at a convenient time and if possible nearby. There is no point in beginning a discussion if you don't have answers and back up!!

If you have a reasonable relationship with the person who is quick tempered, in their moments of rationality is when you should approach them. After a temper explosion is probably when you will be more effective.

After a temper explosion, the person who looses their temper is usually open to more suggestions, and will be more willing to make amends. They will also be coming down from an adreneline buzz. Open up the discussion by asking questions like

Was it worth getting so upset?

Do you like getting so angry?

Are you aware of how it impacts more than you?

(after this give the details, if appropriate)

Would you like to learn how to deal with it?

Asking questions these kinds of question is a calm and reasonable tone

Go along these kind of non confrontational type questions, and ensure that the willingness to do something about the anger comes from the person displaying it. This is why having done your research you will have solutions and ideas. This keeps the whole conversation positive, and the person you are talking to, will NOT feel threatened.

However if you feel that you or someone else is in danger, please consult you local authorities and get the appropriate help. Remember that there is a big difference between having someone in your life who gets angry or has a temper and someone who is abusive. Remember someone who is abusive is NOT reasonable, and no matter what you try to do or say the situation will be made worse.

If you are in an abusive relationship, please get help, there are a lot of people who are so willing to get you out of your abusive situation. They are just waiting on your call. You can also try getting help from a trusted family member or colleague. I can guarantee you, that even though you try to keep it quiet they know exactly what is going on!!!

3-3-09 I wrote this article a while back, and I wanted to add this resource, its about gaining confidence and helping yourself.  Get The Best of You is well worth a look