The most common configuration is to use PostgreSQL's built in master/standby streaming replication. However you will need to develop any fail-over logic you need yourself or use a third party tool such as EnterpriseDB's Failover Manager.
Or use already available open source tools such as Pgpool-II or Linux-HA.
Sincerely, JD
-- Command Prompt, Inc. - http://www.commandprompt.com/ 503-667-4564 PostgreSQL Centered full stack support, consulting and development. Announcing "I'm offended" is basically telling the world you can't control your own emotions, so everyone else should do it for you.