Postgres and geographically diverse replication

Hi,

I've been given a task to build a couple of geographically separate
servers, which are capable of replicating data between each other.

I've surfed through various google results, and most of what I've found
seems to be a bit dated, so I thought I'd pose my question here, perhaps
for more detailed and more up-to-date info.

Is this normally done in a push/pull scenario within the postgres
installations themselves, or is additional software required? What are
the various replication capabilities?

I apologize for the general nature of my questions, I'm new to postgres
and to geographically separate replication. Any tips, books, whitepapers
or other resources you might be able to point me to is most appreciated.

Thanks,

Drew Myers