I'm currently doing some research for an upcoming article here on jazz bassists who have made noteworthy contributions to the music as composers. Obvious examples are Charles Mingus, Dave Holland and Jaco Pastorius, all of whom have penned significant tunes that are a permanent part of the modern jazz repertoire. I'm sticking with a fairly restricted definition of "jazz" here so I will not delve into the pop/rock songwriting category, which would have to include such bassists as Paul McCartney and Sting. I'm also going to leave out folks like Edgar Meyer (IS there anyone else like him?) - classical, folk, country, bluegrass and crossover composers. Those great bass players could be the subject of another piece.
In the meantime, my list of bassist/composers includes: Ben Allison, John Patitucci, Steve Swallow, David Friesen, Drew Gress, William Parker, Stanley Clarke... I am trying to be inclusive of electric players and the wide variety of genres that commonly come under the heading "jazz".
Feel free to add your suggestions for consideration.