Sig 4 star, Hanger 9 Twist (tamed down to start with), Goldberg Skylark (my favorite out of all), Tower hobbies Up-Roar, Tower Kaos, any "stick" style plane. All of these are GREAT second airplanes and I have personal experence with all of them.
If you are using a 40LA the best choice would be the up-roar. The Up Roar is a light weight plane ands will perform well with a smaller engine.
If I was swapping engines and moving up I would slap a 46, 50, 55 or 60 into a skylark.

I know there are others but the small 40 engine really needs a small airplane to enjoy.