I have to admit, this was kind of a fun exercise. I stopped when I hit the 40 or so below. I also took this one step further and sorted by best experience or memory to worst experience/memory, top to bottom. By far my pick for bottom of the barrel, hands down worst airline I've flown is Ryanair.
Like another poster, I also miss TWA. That was my preferred carrier in the '80s, even though I seem to recall their service being a little spotty.
JAL
Air New Zealand
Cathay Pacific
Qantas
Emirates
British Airways (glory days version only)
TWA
Eastern
Braniff
Turkish
TAP
Lufthansa
AirMalta
SAS
Icelandair
FinnAir
Air Seychelles
KLM
Gulf
United
Alaska
American
Southwest
Northwest
Delta
Air Canada
Continental
Horizon
America West
AirOne
Olympic
Spanair
Go
Easy Jet
Swiss Intl
Meridiana
Iberia
Midway - in the '80s they were always, always late out of MDW
SATA
Alitalia
USAir
Ryanair - nuff said