TinyCal is a menubar calendar with Google Calendar integration. It can show multiple months, use custom calendars, and show holidays and personal calendars. TinyCal has many useful features.
Features
☞ Personal Google Calendar integration
☞ Support for Google Calendar Gadgets
☞ Configurable month display
☞ Configurable event display
☞ Custom calendars
☞ Tear-away menu
☞ Growl reminders
☞ Create and delete events
☞ Hot keys
☞ ISO 8601 week numbers
☞ Secondary calendar overlay