Notable Watchers include Rupert Giles (Buffy's Watcher for most of the series) and Wesley Wyndham-Price.
In the Highlander television series, a Watcher is a member of a secret organisation devoted to tracking Immortals.
Warning: Wikipedia contains spoilers
In the "Logopolis" serial (1981) of the television series Doctor Who, the Watcher was a spectral figure that would appear in the distance, watching, whenever something significant happened. He turned out to be a foreshadowing of the Doctor's next (fifth) incarnation, and merged with the dying Doctor at the end of the last episode. His exact nature has been debated by fans, and it has been speculated that certain other shadowy presences that have appeared in the series may also have been watchers.
The Watcher is a mystery novel by Kay Nolte Smith.
The Watcher is the name of a super-powerful pacifist character in the universe of Marvel Comics.