How 'bout Bill Gates and/or Warren Buffet? Sure, they're rich, but both have contributed a total of $26 billion+ and $31 billion+ respectively to the Gates Foundation. The goals of the Gates Foundation include improving the quality of schools across the country as well as eradicating the world’s top 20 diseases, including AIDs, malaria, and tuberculosis. In 2005, the Gates Foundation ranked just behind the country of Finland in global health spending. I believe they have living wills stating that at least half of their fortunes are to be donated to charity.
I don't think any living person belongs on a stamp but who wants to bet we see an Obama stamp before the elections.
The only person who would come close is Bill Gates. Although there could be some question as to how he built his fortune, the fact remains that the philanthropic contributions of his Bill and Melinda Gates Foundation has made a positive affect on millions of lives worldwide.
After looking at all the pattens coin here it's obvious that the US Mint should revisit and make coins with meaningful designs that includes some symbolism. Symbolic and artistic coins are more desirable as long as the mintage is low.
It's real worth would be questionable, marketing could be a problem and the U.S. Doesn't have a Coke Standard to back it!