Any of the Turner Classic biographies are absolutely worth watching.
TB, I assume you're referring to the biographies which air between the films, and serve as commercials. Yes, they are wonderful to watch and very informative.
One of the best things about TCM is the commercials! While every other station on television is busy airing advertisements, TCM's commercials are educating and informing us. Often times I don't even watch the films, but instead await the commercials which educate on every thing from the films and actors themselves, to the processes involved in making films. And of course, some of the commercials, which promote the station itself, are absolute aesthetic works of art in their own right.
