Replicating some tables from one postgres database to another
On PostgreSQL 9.3, you could use postgres_fdw to transparently query the foreign table on the other machine.

On older versions, dblink can be an option as mentioned by Andrew.

Another option is to use a tool like Londiste or Slony-I to replicate the tables you want. I recommend using Londiste for this, it's going to be much simpler. It creates triggers on the table to detect insert/update/delete, and replicates these using its own client/server and a queueing system to the other database, where it does corresponding insert/update/deletes. I use it in production on several client sites and it works very well.

A future option (hopefully in PostgreSQL 9.5) will be log streaming logical replication, logical changeset extraction and bidirectional replication, which will allow individual databases or tables to be replicated at the SQL level. Part of the work for this was committed to PostgreSQL 9.4, but not enough to make it useful for what you want to do.