Best music scribing I've seen recently is this little gem by Sara Bir: Filmed Notes, concerning the idea of the musical biopic. For Hollywood's purposes, Bir points out that an artist's or band's career is shaped into a suitable beginning/middle/end storyline with the inevitable rise-fall career course that VH1's "Behind the Music" documents (too) well now. There could have been more than a few examples that are cited in the article but that would have been a massive undertaking and the few examples there serve the purpose. Other than the upcoming Johnny Cash film Bir notes, there's also a Biggie film in the works.
One difficult thing to chronicle in films like these are the scope of the subjects. By nature, larger-than-life characters are the basis of these films but what also comes along with that are very complex characters that are difficult to fully chronicle in the space of a two hour film- that's usually left to a good biographer. While it'd be boring to see the goody-goody side of a famous character for the space of a film, most of these pics delve into dark sides and a character overcoming this or not without trying to explore or explain where these problems come from in the first place. In fairness, this isn't easy to compress into a biopic and it's usually not done very well in your standard drama.
One way out of this dilemna is a the novel idea of having multiple parts playing one character. This didn't work very well in the recent Lennon musical but a more promising example of this may be Todd Haynes' I'm Not There: Suppositions on a Film Concerning Dylan, which is rumored to have Christian Bale, Cate Blanchett, Colin Farrell, Charlotte Gainsbourg, Richard Gere and Julianne Moore among others playing the Minnesota bard. Still in pre-production at the moment and slated for a possible 2006 release, it may not be as revealing as Scorsese's recent Dylan film but may be more in the spirit of the subject if Haynes structures it right.