I'll second
Brain Wave and Flandry (the Terran Empire) but also van Rijn/Falkayn (Polesotechnic League) which comes earlier in the same future history. I wouldn't even skip
War of the Wing-Men.
This makes up about a dozen novels and a half-dozen collections but the latest Baen printing has them all in seven collections. Also
The High Crusade and
After Doomsday are pretty good but really, you've already read two of the best non-Polesotechnic/Terran Empire novels (
Brain Wave being another). But I'd also recommend hunting down his stories as he wrote a huge number of those and many are excellent. Then again, if you have enough anthologies with enough of his stories, that might do.