Hot Standby/Streaming Replication is available as of PostgreSQL 9.0 and provides asynchronous binary replication to one or more standbys. Standbys may also become hot standbys meaning they can be queried as a read-only database. This is the fastest type of replication available as WAL data is sent immediately rather than waiting for a whole segment to be produced and shipped.
Warm Standby/Log Shipping is a HA solution which 'replicates' a database cluster to an archive or a warm (can be brought up quickly, but not available for querying) standby server. Overhead is very low and it's easy to set up. This is a simple and appropriate solution if all you care about is continuous backup and short failover times.