I like it "Japanese style"
boil potatoes, then cube
add thinly sliced cucumber (use a mandoline) that you've mixed with salt, let sit, and squeezed out the excess water
add apple chunks/small slices
add kewpie mayonnaise (from an Asian market, I don't know if Asian sections in the regular grocery stores have it, though).
salt and pepper
I don't remember if my mom puts in celery...maybe...
you can put in diced eggs, too
I know, apple sounds weird, but it only works with the kewpie mayo. We eat it with ikari sauce (japanese worcestershire sauce).
yum!