I hate to be the first one to mention it, but there was The Highlander : The Series that lasted for a while. Of course, it made absolutely no sense at all in the context of the movie (in which the Immortals were usually in different families, and in which the contest had conclusively ended in the '80s).
La Femme Nikita also became a series.
There was a Planet of the Apes animated series, too.
I think the Clueless series is still in production on the WB or thereabouts.
Mr. Belvedere was another one.
Saying that the comedy series Mr. Smith was based on the movie Mr. Smith Goes to Washington might be unflattering to Jimmy Stewart. Though it’s entirely possible that the upcoming movie Mr. Deeds, starring Adam Sandler, is based on that television series.
X-Men (movie and animated versions)
Hulk (movie and series)
Witchblade (series)
Generation X (made-for-TV movie)
The Maxx (animated series)
Teenage Mutant Ninja Turtles (movie and animated series)
Actually, I think the show based on Barefoot in the Park was called Barefoot in the Park.
A teacher of mine in high school told me that Bridget Loves Bernie was based on an operetta-turned-movie called Abie’s Irish Rose, with the socioeconomic standings of the ethnic groups being reversed (scion of a wealthy Jewish family falls in love with and marries a poor Irish-Catholic girl, and how their families handle the blending).