Depends heavily on how strict the term "clone" is being defined. In the strictest sense, Mario and Manamon are pretty clony. In a looser sense...' I guess some of the FPSes might be considered clones of existing games? Oh, and Shades of Doom might have some things in common with Doom, I dunno. I've heard Swamp described as accessible Resident Evil? Oh, and Space Invaders and games in that category.
A lot of games that try to be direct adaptations differ too much from the source material to really be considered clones. Even Mario might fall in that bucket, given the way jumping works. Pacman Talks, for example, is kinda debatable, because Pacman is a top-down game where seeing the entire maze (or 2/3, at least) is a major aspect of the gameplay—it's more like a high-speed board-game. Whereas Pacman Talks is first person and gives you far less information at any given time, and first-person mazes are effectively a dramatically different genre entirely. So is Pacman Talks a Pacman clone? I'd say nay (for I am a horse, apparently), but you might disagree.