Based on different parameters, reuirements etc you have the following popular options.
- Block level replication – DRBD
- PostgreSQL Streaming replication (SR)– only available 9.0 +
- Slony Trigger based replication – Almost the gold standard for Master – Slave replication
- Bucardo – Perl based multi master Async replication
- pgPool- II – Load balancer, Query cache, connection pooller , Replication manager
- pgCluster – multi-master synchronous replication