I have used "Note Reading Studies for Bass" and recommend it, but the October 2002 issue of Bass Player mentions a new book that might be helpful too. Mind you, I haven't seen it myself.
Essential Sightreading Studies for Electric Bass, Vol. l
Molto Music, $17.95; with CD
http://www.moltomusic.com
Some exercises from the book are are page 85 of the Oct. Bass Player.