I remember 13 of them, especially Eastern. I was an official member of the We Hate Eastern Air Lines club and had a WHEAL button to prove it.
I loved US Air when I was PIT based and belonged to Chairman's Preferred, which was the best FF program at that time: I always flew first class with my companion and the upgrade was at no cost, and if I booked 48 hours in advance, no flight was ever sold out. I occasionally sat in the departure area while they off-loaded someone else so I could get on.