<apex:inputField value="{!Event.showAs}"/>

<apex:selectList value="{!Event.ShowAs}" size="1">
    <apex:selectOption itemValue="Busy" itemLabel="Busy"/>
    <apex:selectOption itemValue="OutOfOffice" itemLabel="Out of Office"/>
    <apex:selectOption itemValue="Free" itemLabel="Free"/>
</apex:selectList>