Held items pretty much revolutionized competitive battling. A lot of Pokemon are usually only viable because of their held items. Ironically, even strategies like Acrobatics, which don't rely on items, still rely on items haha.
I really like the concepts of Absorb Bulb, Cell Battery, Snowball, and Luminous Moss (could be more, don't remember). Although they're never really used, I kind of want to use it just to see how my opponent would react.