There are two basic types of euthanasia: active and passive, Active refers to killing with a toxin which is what Dr. Jack Kevorkian did, and was jailed for. 

Passive euthanasia refers to withdrawal from a life—sustaining treatment. The precise definition of life sustaining treatment  is subject to controversy, with many making a distinction between providing food and water via a tube and the greater intervention involved in more complex medical interventions. 

Independent of this, euthanasia (whether active or passive) can be voluntary (in accord with the patient's expressed wishes), nonvoluntary (where the patient is unable to express his desires) and involuntary (where the patient's desires are overruled).

Dr. Kevorkian performed voluntary active euthanasia disguised as physician—assisted suicide.

The case in the movie Million Dollar Baby was voluntary active euthanasia (if you believe the adreneline killed her) or voluntary passive euthanasia (if you believe that the removal from the ventilator killed her).

Terry Schiavo's case, in contrast, represents clear passive euthanasia which is voluntary if you believe she wanted it, involuntary if you believe she wanted to live, or nonvoluntary if you believe there is no evidence of what she wanted and the decision is being made for her. I believe the safest category in her case is nonvoluntary passive euthanasia.

What is illegal in our society is any kind of active euthanasia (passive voluntary euthansia is legal; it is withdrawal of life support), though our studies show that people do not care so much about this as fearing nonvoluntary or involuntary euthanasia, whether it is active or passive. The danger of legalizing active euthanasia of any kind is that it can rapidly degenerate into involuntary euthansia (which is done against patient's wishes—which was done in Nazi medicine) or nonvoluntary euthanasia which is what seems to be going on with Terry Schiavo.   

Much of what some people want to be legal, already is. 
So, in summary:

Voluntary passive euthanasia:  already legal
Nonvoluntary passive euthanasia:  indeterminate
Involuntary passive euthanasia:  illegal
 
Voluntary active euthanasia:  Illegal except for Oregon, Netherlands, Belgium, and previously in the Northern Territories of Australia, and practiced in Michigan by Kevorkian.

Involuntary active euthanasia:  illegal but seems to have been practiced on occasion in Netherlands.

Nonvoluntary active euthanasia:  illegal but seems to have been practiced in Netherlands.
 
However, voluntary euthanasia is a difficult concept, because people can become demoralized and depressed and thus seek it out. To say it is legal is not the same as saying it should be encouraged. 

I once ran a suicide prevention clinic.  We tried to change people's minds about killing themselves, even though the act would be voluntary.  Kevorkian did not do this but simply went along with patient's requests, or maybe even encouraged them.

This is merely a very basic taxonomy. Circumstances are always full of complications which make even this set of distinctions quite murky.

Kal Kaplan is a professor of psychology and director of a suicide reasearch center. He was psychologist on the Detroit Free Press—Wayne State University study of the Kevorkian cases.