Two things:   clean water; and vaccinations. 

Clean water (clean drinking water and proper removal of sewage) prevented the ingestion of disease-causing organisms.  There are many examples of this but the bedrock event was John Snow removing the pump handle during the cholera outbreak in London. 

Vaccinations have also reduced disease and human suffering for obvious reasons. 

People tend to forget the impact of these two things because no one in living memory remembers the time before they existed (although lack of clean water and lack of vaccinations are still prevalent in some areas of the world). 

Although not really technologies, WHO  Global Risk Factor and Burden of Disease Studies show that prevention of child and maternal malnutrition , abolition of tobacco smoking and control of HIV contribute most to overall global health improvement .

For technologies,I would vote for antibiotics and CT/NMR imaging as the most significant in the last 100years .

It might be an idea to make this question more precise: most important health technology at what time and for what population. Sanitation was historically most important (see cholera epidemic in London and John Snow) but soap is a great technology against all kinds of skin diseases. In some developing countries these technologies still play a role, as does adequate nourishment including before birth. As for the most important technology to improve health in let's say the G8 countries , it might be techniques and policies to increase the level of exercice and to decrease the BMI. 

Thank you so much for your answers. I agree with Edeltraut Kröger that I should make my question more precise. But on the other hand, your answers inspire me to think wider. What I might have meant was computer based health improving technology, since that is the field I work within myself. But a more open question may point toward more innovative solutions.

For the last 5 years I have worked with music therapist, and they talk about music as a technology, technology of the self with reference to M. Foucault. And they look into the music score for affordance in the music. Further the music therapist I have worked with, base their discipline on a humanistic and resource oriented health approach, not focusing on diagnosis and weaknesses, but on strengthening the clients own resources. For me as an industrial and interaction designer that has inspired me to take design from a very task, function and goal oriented way of thinking, to a more open, diverse and possibility oriented design thinking. It has changed my way to design and think about design, which never was the goal, but for what I always will be grateful.Therefore I am thankful for your answers, even if I might rephrase my question to:

What is the most innovative health improving computer based technology you know of? 

But still open to what other peoples interpretation and perspective might take me.

Yes, using Information Communication technology is an innovative one. For instance, the Integrated Health Information system contributes a lot for the improvement of health care delivery. Likewise, the supply chain management of drugs are the other. In India there are efforts to improve the the health information using ICT in recent years. The IDSP on surveillance of diseases started with a good intention. Likewise, HMIS of TB program called RNTCP is another successful model. Likewise, ICT contributes a lot to public health.  

Hi there, this is getting really interesting. Music therapy may have much more to offer than we are aware of but I take it that you are not really interested in clinical or brain research on the healing potential of music. With regard to computer based health technologies, many are being experimented now and also implemented, e.g. cell-phone apps to help with medication adherence, depression treatment in children, diabetes surveillance etc. The problem with the evidence base is that high quality RCTs cost money and time, so when doing systematic reviews, oftentimes these technologies can't be rated. I'ld say an interesting one right now is also the e-cigarette. Some reviews re starting on evidence regarding those. This is an exciting field of research to be in :-)

Return to food from the oceans, because all life started in the sea: that would be innovative, as most people have forgotten that