Liferay is a good option , but before you go any further , take a look at 3 other open source portal system.
Sun Microsystem Portal at : portal.dev.java.net
StringBeans portal at :
www.nabh.com and certainly Exo portal at :
www.exoplatform.org I have experiences with stringBeans and i think it is a good portal after all.easy to setup , very easy to manage , the feature set and pre-bundled portlet make it a good choice.