I'm with Boplicity (and like him I'm a confirmed bibliophile).
It took me awhile but I grew to love Di Bartolo's Serious Electric Bass, for scales and modes. This is particularly good for the "5 position system" that some folks are trying to sell as a brand new and innovative way to learn the bass.
Levine's Jazz Theory book for the fundamentals of Jazz (even though it's still too advanced for me, I can see spending the rest of my life on it).
Gary Willis's Fingerboard Harmony for walking.
Wyatt & Shroeder's Harmony & Theory for the general theory.
But to tell the truth, I've learned the most from transcribing songs I like. I thought buying books would make me a better player. But no matter how many times I practice a scale, and no matter how many lessons I took, I never really felt like I could act as a bass player in a band. But now that I'm jamming with a guitarist and in a cover band and transcribing all these songs, I finally feel like I'm getting somewhere. So maybe you don't need a book, just listen and transcribe.
Just my two cents.
