We want some trees and crab apples seem like a good choice. They are relatively small and spend most of the year either decorated with blossom or fruit. The fruit is not edible to us raw (although the neighbourhood birds will appreciate it!) but will be great for crabapple jelly as well as a source of extra pectin for other preserves.
Malus x scheideckeri ‘Red Jade’ and Malus trilobata are two particular versions I have in mind, although the popular ‘John Downie’ might be a good choice as well, being renowned for producing lots of fruit.