Edit: Even the main Tylenol page links is ambiguous: https://en.wikipedia.org/wiki/Tylenol

It's a wiki, so I'll guess I'll add it.

Kleenex, Google, Band-Aid, Post-It, Q-Tip, and Sharpie are all in a dominant position in their respective product categories. Off-brand examples of all of them exist, but all of my Sharpies are Sharpie brand, I use Q-Tip brand Q-Tips, I only Google with Yahoo or Bing when Google itself is down, and My Band-Aids are Band-Aid brand adhesive bandages.