They also have $50 off coupons from time to time and they just released a new one for flights to Europe and Africa from the US.
It can be used for all bookings made on lufthansa.com for these destinations between October 9th and October 15th. Travel must be between November 1st and January 6th.
The coupon code is Z616RRJ8RD8T.
It's valid for all Lufthansa Group carriers (inc. Swiss, Austrian and Brussels) but also on United and Air Canada!
If you are in the market for a fare to Europe or Africa on United or Air Canada, see if the same fare comes up on Lufthansa.com (as very often it does!) and apply the voucher. It seems there is one per ticket – so for multiple tickets you can get $50 every time.