One thing to consider when traveling: some countries will not admit visitors with passports expiring within six months or will not put visas them. So, check with your destination and renew accordingly.
Link for U.S. passport questions: http://travel.state.gov/passport/fri/faq/faq_1741.html.
Link for UK passport questions: http://www.direct.gov.uk/en/TravelAndTransport/Passports/Renewingorextendingyourpassport/DG_174096
Link for Australia passport questions: https://www.passports.gov.au/Web/FAQ.aspx