No Theme Tune

Only very rarely does a show have no theme tune whatsoever. However, many recent Anime series have left out the OP in the first or last episode (or both).

Current trends seem to favour the lack of a theme tune, particularly in sci-fi/fantasy drama series, such as Lost, Heroes, Supernatural, Invasion, Surface, and Threshold.

Examples of No Theme Tune include:

Live-Action TV

One of the earliest examples is Pearl, the opening credits of which consisted of a hand writing the show's name on a chalkboard, with no other sound audible.
Until the 1980s, network newscasts in the U.S. had no opening theme songs. Then each network started using its own bombastic fanfare (NBC's was written by John Williams). Some consider this the point where newscasts started becoming more entertainment than news.
Lost has no distinct theme song, just some sound effects and a few notes playing over a flying graphic of the show's title.
- Particularly amusing is that on the Soundtrack, this is cited as being "Composed by J.J. Abrams". 16 seconds of sound effects is composing, is it?
Murphy Brown did not have a consistent theme, but would frequently open with a Motown song in which the lyrics would be relevant to the events of the episode.
Seinfeld also had no real theme song, only the music stings heard at the beginning and throughout any given episode.
- Although it was used in the ending credits, this song is considered the "theme song" of the show (the musical stings are basically snippets and variations of it).
Surreal/downright weird UK comedy series Jam had no theme, only a bizarre monologue from creator Chris Morris, always ending in "Then Welcome... In Jaaaam".
The Aussie cop drama Scales of Justice didn't have a theme tune... because it couldn't afford one (article from The Age).
The second season of My Name Is Earl has taken to just using the final chord from the original theme tune with the final shot of the original opening sequence, with Jason Lee (who plays Earl) saying in voiceover, "My name is Earl."
Jericho shows the show's name with the sound of a radio tuning amid static.
- With brief messages given in Morse code.
Breaking Bad has a title sequence that lasts about five seconds, consisting mostly of an animated title card accompanied by a short musical clip.
The Britcom Porridge, set in a prison, is unusual in having no opening theme. Instead the opening title shows a montage of prison cell doors banging shut, accompanied by the voice of the judge (voiced by Ronnie Barker) passing sentence on prisoner Norman Stanley Fletcher.
Burn Notice uses an Opening Monologue.
Castle has a sort of introductory musical sting, but no real theme. The credits play over the first act.
Both Stargate SG-1 and Stargate Atlantis originally had cool orchestral theme tunes, for the ninth and second seasons respectively this was done away with in favour of a very short snippet of if in front of the show's name. After Fan Outcry the theme tunes were very quickly restored. However, Stargate Universe goes the Lost route of just having a brief music sting over the show's name.
Grey's Anatomy, which once had a theme tune by Psapp, no longer has a theme tune, instead showing the white background with the title in black show up for a few musical blips from the former theme.
The title for 24 is the number 24 blinking into view on a digital display with sound effects, followed by a rundown of the plot thus far composed of clips from previous episodes. (There actually is a 24 theme that was used in the beginning of the pilot and serves as a sort of leitmotif throughout the entire series' score.)
As noted in the trope description, Supernatural. The title is thrown up on the screen and a short sound plays, differing between seasons.
60 Minutes. But the ticking stopwatch is sufficiently iconic, it seems.
My Wife and Kids would jump right into the episode, with the title of the show and a short musical sting that changed frequently.
Glee, interestingly, has no theme song, despite being a musical show. Just the title in lowercase on a black background with the crescendo of the music from the previous scene over it. Once, it was Mr. Shuester's license plate, despite being done normally later in the episode.
The later seasons of Everybody Loves Raymond didn't have an intro sequence; they would just superimpose the title of the show over the action, already in progress.
Columbo was the only Mystery Movie element to get by without a theme tune (the end credits for each episode usually featured music from that story's score; not until the '90s instalments did Universal try - and fail - to have "This Old Man" as a theme).
Being Human (UK) usually just slips the Title Card in when it's reached an appropriate point.

Radio

The Goon Show is an unusual example of a Radio comedy show with no opening theme. After the opening announcement ("This is the BBC Light Programme") the show launches straight into this week's absurd plot. The show did have a variety of closing themes over the years, though.

Professional Wrestling

When the New Age Outlaws started teaming in WWE, one thing that made them stand out from the other wrestlers were their lack of an entrance theme. The only thing heard as they walked to the ring was Road Dogg talking trash about their opponents. They got a theme after a few months though.

Puppet Shows

The '60s version of Captain Scarlet opened with a voiceover followed by gunshots and a vaguely comic sound of someone getting shot offscreen. The nearest thing to a theme tune was in the end credits.
- There was a musical 'sting' and harp glissando at the beginning of the title intro, followed by quiet electronic tones not unlike the 'Mysteron' theme used in the episodes, over the stalk through the alley. Not to mention the drum-beat scene-change to the episode beginning.

Web Original

Lonelygirl15 has no theme tune; since it's presented as a series of video blogs, almost all the music on the show is either diegetic or indie.
- The same is true of LG15: the resistance.

Western Animation

Regular Show begins with the title card and a one-second synth sting.
The Amazing World of Gumball just has a few notes over its title when it airs in the U.S., but that's just the end of the original opening which was cut for time. Other countries either show the original opening, or ones they made themselves.
Secret Mountain Fort Awesome don't have one either, just a title card accompanied by a yell.
Cartoon Network seems to be making this the standard, as even their half-hour action cartoons like Green Lantern: The Animated Series and Young Justice from the second season onward lack much besides a title card.
Beavis and Butthead only has a jingle that plays during the title cards.
Home Movies only has the title and a very short piece before the episode.
Ugly Americans just has a title card with some sounds played along.