Peas just aren't worth it. They're a pain to trellis, the pods are hard to spot, shelling takes forever, you have to plant a lot to get a decent side dish, and they need their own space since they come just a little too late for me to want to harvest then replace with a summer veggie.
Bell peppers aren't prolific enough to justify the space. At least they haven't been in our garden. Ditto with eggplants.
Melons do not succeed in our garden, for whatever reason. I blame the bugs.
Cabbage and other cool weather crops don't like DC weather and get eaten by bugs.
Potato plants also don't give a whole lot for the space they take up. But they are fun.
Fresh lettuce is great but cleaning the leaves is time consuming and starting them from seed can be tricky. Some of the seedlings will die for no apparent reason.