Two suggestions. Palau and/or Yap (Federated States of Micronesia). Especially if your dive certified. These places are amazing with some great local culture even if your not a diver. Only draw back is its a long trip, but its off the beaten path for Americans so its sure to be a one of a kind trip. Both islands are reached by United through Guam.
A couple of suggested stays...
http://www.palauppr.com/default-en.html
http://mantaray.com/