Wikipedia has a nice section on the history of said memristor. Apparently, its discovery goes back to 1960 with work by Bernard Widrow (Professor Emeritus, Stanford). A few patents are coming out of this. http://en.wikipedia.org/wiki/Memristor#Timeline_of_memristor...

One of the patent awardees, Blaise Motett, seems to have a different view of HP's memristor, namely that their sr is not actually one. http://www.slideshare.net/blaisemouttet/mythical-memristor