Porter Airlines seems to be quite generous with its 60% promotion. Though these tickets seem to be very limited, so if you know when you plan to travel and see the offer, I would jump on it as soon as possible.
For this promotion, you will need to make your reservation by
January 13, 2015 and fly by May 13, 2015.
There are certain conditions to keep in mind, such as up to 21-day advance purchase may be required. The blackout dates are February, 13 and 16, 2015, as well as April 1-7, 2015. The 60% discount only applies only to the regular base fare and not to fees, taxes or surcharges.
The price you pay is non-refundable but you can change your itinerary for a fee of up to $200 per person per direction, plus any fare differential.
Remember that when you fly with Porter Airlines, you can earn VIPorter points. The biggest issue I have with this program is that the points expire 4 years from their earning date. Hopefully Porter will eventually change its expiry policy. I would like to see something like, there needs to be an activity once every 18 months to prevent the points from expiring.