All of the ones I can think of are specific products that have come to represent their kind. This is usually either because it is the first of its kind, as in a Xerox machine (the first office photocopier), or it arises from popularity, as in Sharpie or something like "Google that" (though I'd say that's a bit informal/debatable).
Other examples I can think of off the top of my head are:
- Kleenex
- Post-it