Off the top of my head, mainstream sedans that had a coupe version in 1990, ignoring hatchbacks:
Buick Skylark
Buick Century
Buick Regal
Chevrolet Cavalier
Chevrolet Corsica (Beretta)
Chevrolet Lumina
Ford Tempo
Honda Accord
Mazda 626 (MX-6)
Mercury Topaz
Oldsmobile Cutlass Ciera
Oldsmobile Cutlass Supreme
Pontiac Sunbird
Pontiac Grand Am
Pontiac Grand Prix
Volkswagen Jetta
Probably missing a few too. Later in the '90s a bunch more came too. Colt, Camry, Civic...