Long Form Promo

What happens when the Vanity Plate meets the Music Video—a two- to three-minute film extolling the virtues of whichever network it's running on, usually run during off-peak periods (late at night, or as filler after a long-running live event).

In this case, the TV audience isn't the most important target; long-form promos were meant to be seen by people with money to spend on ads, and many were produced as one part of a much longer, Infomercial-like promotional video distributed to the affiliates and ad agencies. Given that, the networks spent lots of money on these; depending on the network, it could be a few clips from shows edited together in a fast-paced style, or on the other extreme, it could be an entire short film with network stars playing most of the roles. All this went together with a Jingle that was often as well produced and catchy as a pop hit on the radio; state-of-the-art animation often came into play as well. Promos like these were some of the first uses of Scanimate and digital 3-D rendering back in the 1970s and 1980s.

After cable started taking over around 1990, this practice waned because the broadcast networks didn't want to spend the money as their market share declined. Networks still do the promo packages for advertisers, and still "redress the set" every fall with new graphics, but in general, long-form promos are rarely seen on TV anymore.

Related to the Station Ident; the graphics used for idents were usually based on the graphics introduced in these promos.

Examples by country:

United Kingdom

The BBC is quite big on extended self-promotion pieces, some of which have admittedly been rather cool.
In the late 70s, after ITV had been off the air due to industrial action for a couple of months, the network went back on the air with the "Welcome Home to ITV" promos.
In 1990 Sky Television ran the "We're the One" promos, later followed up by "Still the One", as part of an aggressive marketing campaign to get people to subscribe to Sky rather than BSB. The songs were actually based on late-1970s ABC promos from the US, but they seemed to do the trick - BSB went bust after six months and had to merge with Sky.

United States

ABC had the most (and most expensive) examples, starting with This is the place to be in 1971 (which used the Stargate effect from 2001: A Space Odyssey to make swirling, streaming ABC logos). That network's last campaign of note was It must be ABC in 1992, though it still has a slogan for each season.
CBS ran a close second, especially after ABC started winning in the ratings after 1977.
NBC got into this in the late 1970s with its ill-advised Proud as a Peacock campaign; by the mid-1980s, NBC was flying high and telling everyone to Be There. Its last big campaign was The place to be in 1990.
The WB did this ad nauseum in its first season, with promos featuring the old Looney Tunes character Michigan J. Frog, as well as singing and dancing by the stars of such flagship shows as Unhappily Ever After.
UPN did one for its first season as well.
A few local stations have made their own promos in this vein, especially the New York and Washington affiliates, as well a few particularly well-off independent stations.
Several years back, the Syfy had a minute and a half long promo featuring clips from its (then) signature shows being shown over rock music.