Even with the greatest respect for John Adams, it's a bit jarring to see his picture directly next to Bach's, but that is the power of the alphabetical order. They and dozens of other notables are well represented on BBC-3's wonderful Discovering the Great Composers website.
Besides covering individual composers, such as Béla Bartók and Shostakovich with rich selections of music and biographical/musicological information, the site also covers large topics — "The Story of Music" and "Opera Guides."
More about BBC-3: the Thursday/Friday opera matinee this week is Meyerbeer's L'Africaine from La Fenice, acts 1-3 on Thursday, the rest of the opera on Friday; afternoon in London on both days means 6 a.m. starting time on the West Coast.
Timing is better on Friday, Elgar's The Dream of Gerontius, Mark Wigglesworth conducting the BBC National Orchestra of Wales, beginning at 10:30 a.m. PST.