Every bassist needs (IMHO) at least a light overdrive pedal and a tuner on their board! A good cheap tuner is the Korg Pitchblack. Overdrives - there's the EHX Bass Soul Food, EHX Glove, Digitech Hardwire CM-2... tons more options if your budget is higher.
Filters are one of the most fun effects to play, but you might not have much use for them depending on what music you play. I've tried tons and my favourite is the old EHX Mini-QTron that you can pick up pretty cheap used if you're lucky.
Depends what other effects you fancy! If you've never tried chorus, flanger, phaser, octave, delay, reverb, filter, etc, get a cheap multi fx like the Zoom B1on (that comes with a tuner, looper, drum machine, 100 FX and is also a headphone practice unit with aux input) to see what you're into.