You’re looking too narrowly: psychology is much bigger than social psych, and a lot of the sensory or perceptual stuff has held up astonishingly well.

In addition the things NPMaxwell listed, consider these theories/ideas: Weber/Fechner’s law, parallel vs. serial visual search, categorical perception, attentional selection, semantic priming, the coarticulation of phonemes, spatial frequency channels, and properties of sensory receptors, to name a few.