I had heard of a few Father's Day Freebies, such as:
Spaghetti Warehouse - Dad eats free with the purchase of an entree
TCBY - Free Cup or Cone for Dad
Cleveland Metroparks Zoo - free admission for Dad I'm assuming more zoos participate, check with your local zoo. Also, I have heard that some National Parks are offering free admission this weekend.
But, for a more comprehensive list, check out this post at The Thrifty Mama.