Gee, thats a tough one (for me).
He's already got one of the best powersets. He's an omnidisciplinary genius, he can shrink/grow himself, he can shrink/grow other ppl and objects, he can "talk" to insects...
Maybe a variation on microscopic vision? The ability to look at someone/something down to the molecular level and see what makes them/it tick? That might be useful.
Either via his own eyes ("constant exposure to Pym Particles has altered my ocular lenses...") or a new invention ("hey check out these cool new goggles i made...").