Up 'til last year, when I had to give up my allotment - I grew Mennonite climbing beans, a reliable heritage variety grown for eating fresh and drying for winter stews.
Peas can also be saved, I've grown and successfully saved a few heritage varieties over the years.
Also tomatoes that started off as Crimson Crush. Saving seed of these, each year - gave me slightly smaller fruit than the original size, but the plants still had a fair bit of blight resistance..
Tromba d'Albenga squash doesn't cross with other varieties, so you can save seed for that, as well.
I'm sure there are more...