I personally would not say 4 scales, but the 4 arpeggios that will cover the majority of your bass playing are the Major, minor, Dominant and half-diminished (min7b5). You should know how to play these starting from any finger as well as how to play their inversions. In every key, all over the neck. Extra credit for knowing the notes of each chord!
This is excellent advice. Just wanted to flag it for serious players.
 
I'm certainly going to get whatever I can buy which is to say every book I see.
This is bad considering I love punk music and dee dee ramone basically played a box around the c on the a string lol in going to be playing matt freeman style I hope I didn't like rancid until I started playing bass and heard him now I can't get enough.