Calculated column for Active/InActive depending on end date

Create Calculated column in list and paste the below formula there,

=IF(OR([End Date]="",[Today]<[End Date]), "Active", "Expired")

This can be useful to mark the item which has reached its expiration or end date.

Please find more formulas for Calculated field here,
http://msdn.microsoft.com/en-us/library/bb862071.aspx