Abel, Carl Friedrich 
Grove Concise Dictionary of Music entry at WQXR radio focusing on his collaboration with J. C. Bach and his bass viol playing and composing.
http://www.wqxr.com/cgi-bin/iowa/cla/learning/grove.html?record=14Classical Music Archives: Abel
Sound files in MIDI format.
http://www.classicalarchives.com/main-a.html#ABEL
Karl Friedrich Abel
Free MIDI audio files from On Classical/Kunst der Fuge.
http://www.kunstderfuge.com/midi-a.htm#Abel
Wikipedia: Karl Friedrich Abel
Biography of the German composer.
http://en.wikipedia.org/wiki/Karl_Friedrich_Abel
HOASM: Carl Friedrich Abel
A couple of portraits and a brief biography of the German composer and viola da gamba player. Includes a partial discography.
http://www.hoasm.org/VIIJ/Abel.html
Carl Friedrich Abel
Summary of musical style and output, biography, and portrait painting from the Classical Composers Database.
http://www.classical-composers.org/comp/abel
