Google offers a free plug-in for Google Apps Premier and Google Apps Education users. The former requires you to pay an annual fee for the Google service. The latter is for schools, universities, and other educational institutions.
What do users with free Google or Gmail accounts use to sync their data with Outlook?
If you’re looking to sync just your default calendar, Google offers a free solution called Google Calendar Sync. If you’re looking to sync calendar and contacts, CompanionLink has a solution called CompanionLink for Google. It also supports multiple calendars, sync to separate Outlook categories, and the ability to exclude personal data from syncing with business data.