It would be pretty easy to knock off all water-borne diseases. Distribute existing technology to clean water where it's needed, or use that newfangled thing that Dean Kamen has.

Bribe all genociding warmongers (e.g. in Sudan) into retirement. Pay for relocation and land redistribution of affected ethnic groups.

Immunize all children in the USA.

Then, with the other 600 billion, I guess you could throw an awesome party.