Self-Improving Artificial Intelligence. Sure it might be the downfall of the human race, but in its place will be a far more intelligent race with more potential than we would ever have. Bonus points if we're able to integrate it with our own minds, creating an interconnected human hive mind.

Longevity.

Stem cell research.

Affordable bionics, because my knees are F'ed!

But seriously, imagine the practicalities of exoskeletons, perfect eyesight, limb replacements, limb enhancements, brain implants.

We can produce as much food and address practically poverty right now. We have never experienced this much abundance of food, wealth and information ever.

If I had enormous amounts of money to aid scientific research, it would not all go to one place but would be spread among several areas.

Space exploration and associated technologies

Genetic applications in medicine

Nanotechnology with an emphasis on medicine

Robotics and artificial (I prefer the word 'synthetic) intelligence

Astronomy and associated disciplines

Cures in the area of mental health issues

A virus strain that wiped out stupidity.

food and clean water? natural medicines. the best recliner ever.

Where does one begin? Disease cures and prevention. Space travel. Dealing with climate change (forget trying to reverse it, that ship has sailed, cheaper to deal with it). The list would be extensive, there are so many worthwhile pursuits.

Space exploration and Terra-forming.