Cut and come again salad plants?

MovingForwards

You've got a good start with those and can keep looking in various places for others to fill out your salad.

Sapindus

My favourite salad plants are corn salad and musk mallow.  Both have a very mild, even furry sort of taste/texture, and both seed themselves around the place so you never need to buy again.  The musk mallow I didn't even sow in the first place, it just arrived, and I thought 1) ooh that's pretty I'll leave it for the bees and then after a while 2) I think you can eat that!
Dandelions are also good if you soak them in cold water for a short while to get rid of the bitterness.