First of all, Entourage is an outdated app on the Mac, the new Office for Mac 2011 comes with Outlook. I strongly recommend against Entourage, its outdated mail storage architecture does not play well with Time Machine, Apple's backup tool, or other backup software.
Either you should look at Apple's Mail which is included with OS X and very powerful or Outlook 2011. To be honest, I would recommend OS X Mail over Outlook 2011, also because it's much better integrated with all other system services. I find Outlook very ugly (it has a Mac adaption of the Ribbon interface which I don't like) while Mail is much cleaner. Also calendar and contact sharing across devices is easier if you use Apple's built-in apps (e. g. if you have an iPad, your calendars are automatically kept in sync). In fact, with the Calendar, you don't even need to use the built-in Calendar app, almost all calendar apps for the Mac use Apple's calendar on the backend, so syncing still works without you having to do anything.