I did several unusual veg last year:
kohl rabi - loved it. Diced, raw, mixed in with diced (cooked) beetroot, greek yoghurt and some horseradish.
florence fennel - all bolted. I read to plant little and often, and some of them will succeed. Trying again this year.
celeriac - grown that for many years. Love it in mash during the winter (with swede or potato)
salsify - nice taste, fiddly to prepare, not much harvest per unit area. Gorwing again this year, but not sure it is worth it
scorzonera - disappointed with the taste, not bothering this year. Have left some roots in to grow on for a second year to try them next winter.
hamburg parsley - I've read about it! not grown it ...
silver chard to replace spinach - all our silver chard was eaten by birds last year. The Ruby and Rainbow Chard were fine (and tasted great, and the plants kept going all summer long ...)
Asparagus Peas - I don;t think we were religious about picking them often, and small, enough. Will try again this year. Does mean that you need quite a few plants though, otherwise each harvest (of very small pods) is too few to make a meal