If you're cooking something which works well with potatoes, like a soup, or a stew, and you've accidentally added too much salt, simply add some potatoes. They tend to absorb the salt.
Once, I was preparing Medias (see link), and accidentally ended up using a cheese which was considerably more salty than usual. So, remembering this tip, I added two medium-sized potatoes, cut into wedges and it really worked well -- in fact, I liked the combination so much that now I sometimes intentionally prepare Medias this way (that is, with potatoes, not too salty) and serve it over rice.

