One of there things I was able to do was to set a discount code that would give a customer who "placed an order over $50 free shipping on a specific shipping method".
Currently the discount control panel does not allow free shipping -However....
*This will require Custom shipping or Realtime/Custom shipping to be in use.
There are two ways to do this. If you presently have custom methods you may use your existing custom 'ground' shipping method. If you don't have one create a ship method called 'Free Ground Shipping'.
You'll want it set to go by 'Price' and then simply place in the 'low price' of $50 and high price of '$99999' with the shipping cost of '$0'.
Depending on how you do this you'll either modify your existing shipping method to give Free Shipping on orders over $50 (or any amount you choose) or you'll add a new shipping option which will give free shipping if the customer selects it (but will only appear when a order is over $50)
I'll try to help out in any way I can if you have any questions on this "How Do I..."