The most "normal" sound effects that I'm having trouble finding are detailed melee combat sound effects. Things like X weapons hitting Y armors at various speeds and angles, either penetrating or failing to penetrate, several variations of each combination for variety.
Less normal, more specialized, and much harder to record would be animal sounds. Complete, accurate animal sound sets for as many individual species as possible. Especially for songbirds, where closely related species can have totally different songs.