For the longest time I thought a certain soda I used to drink growing up, Jones Soda, was discontinued until maybe a year or so ago. Found it in a store near where I live and am glad it still exists.
As for something that actually was discontinued/cancelled, my personal pick would probably be Batman Beyond because I really like the idea of the whole Batman of the future being a teenager who has help from an elderly Bruce Wayne and really like the show in general. I also absolutely love the theme song and animation that went with it.