I've been wanting to improve my reading skills for several years now. A couple years ago, I picked up "40 Progressive Studies for Trombone" on a whim. Not everything is pertinent to bass guitar in here and some of it is just plain hard but it is a great resource for anyone wanting to work on reading!
Having said that, does anyone have anything else written for trombone that works well on bass? It could be studies/etudes or it could be music specifically written for performance.
Edit: forgot to mention that Bach Cello Suites are great too! A bit of a learning curve (don't start on these!) but good way to learn harmonic structure!
I read from my Arban's trombone book when my bass reading skills need some polishing up. It's a good change up to read music that wasn't written for the instrument you are playing.