While published transcription books are great (I do own some), and allow you to see what players are doing at a level that may be too high for you to transcribe (LaFaro, Gomez, etc), you won't accumulate improvisational vocabulary and ideas in the same way as if you do the transcriptions yourself. Books like that are great because they can show ideas that you wouldn't otherwise transcribe, or turn you on to recordings you've never heard. Doing your own transcriptions really trains your ear (melodically, harmonically, and rhythmically), and gives a deeper feeling for the solo (or bass line), because you listen to it so many more times with deep focus. Listen to the solo a bunch, and be able to sing a phrase in good pitch before you put it under your fingers, it makes it so much easier. Good beginning transcriptions (meaning solos and bass lines that are harmonically and rhythmically 'inside') are just about anything by Ray Brown, some Paul Chambers, Mingus' live quartet recordings (Live at Cafe Bohemia, Mingus Quartet plus Max Roach) are fairly easy as well.
Those books are great though for looking at stuff that's much more modern (LaFaro and Gomez, for instance, as mentioned above), and there is a wealth of knowledge in them, and they really kick your butt if you try to sight read them (aaahhh!!!).
