JOSE CHUNG'S FROM OUTER SPACE
Season 3, Episode 20; 1995.

The cleverest of the 'post-modern' X-Files episodes, with Scully interviewing a writer who has an interest in UFO stories -- and a Rashomon-like series of alternate versions of the truth coming out, involving Men in Black, government conspiracies and the possibility that it's all a put-on. Chung (Charles Nelson Reilly) returns in the Millennium episode 'José Chung's Doomsday Defence'.


HOME
Season 4, Episode 2; 1996.

The most gruesome horror show ever aired on mainstream US TV (and often censored in repeats) and a rare X-File in which sheer human nastiness is at the bottom of the mystery. It's inbred-mutants-on-the-farm territory, and manages to compete in the Hills Have Eyes/Texas Chain Saw Massacre stakes.


UNUSUAL SUSPECTS
Season 5, Episode 3; 1997.

The Lone Gunmen showcase episode, a period piece set in 1989 (when Mulder's cell-phone was the size of several bricks) at a hackers' convention in Baltimore, this gives comedy characters (especially Byers) depth and boasts a guest shot by the great Richard Belzer as Detective Munch, the character he originated on Homicide: Life on the Street and holds a trivia record for reprising on more other crossover shows than anyone else has managed (Law and Order, The Wire, The Beat, Arrested Development, Law and Order: Special Victims Unit, Law and Order: Trial by Jury).


X-COPS
Season 7, Episode 12; 2000.

A parody of the reality TV show Cops, this has a TV crew following Mulder and Scully around a bad area of Los Angeles as they deal with a shapeshifting killer that can appear as whatever its victims fear most. It's a neat pastiche, but also offers a surprisingly good monster-of-the-week story.


HOLLYWOOD A.D.
Season 7, Episode 19; 2000.

Writer-director David Duchovny's supreme in-joke show takes place on the set of an X-Files movie starring Garry Shandling and Téa Leoni as Mulder and Scully, with the originals on hand to give advice on tricky subjects like how to chase a monster while wearing high heels.