Originally Posted by bongomania
Honestly, I would stay as clean as possible most of the time, for best compliment/contrast to the synths. Then occasionally step on a squalling flanger or other dramatic effect as a momentary sort of riff, fill, or response.
This might be the best advice. It'll be important for you to listen closely to whatever the synth is doing. It'll be easy to have competing frequencies that'll create resonances and "muddy" up your sound fast. The best thing to do is to actively play an octave away from the synth whenever possible. I suggest listening very critically while playing with the band and trying to figure out how you can play or, more importantly, NOT PLAY as to best serve the song and the sound.
My first thought with the songs that I heard is that if you start putting effects on your bass, it'll compete with the synth. On the song that comes up on your link, I think I'd go get a drink or maybe just play some percussion. Not playing on a song is OK, and many musicians are too sensitive and/or have too big of an ego to realize this. If that's what the synth player is going to play for that specific song, I'd probably pick up a different instrument and try to fill out out the sound.
Judging from that song and the "Protest Song," they honestly may not need a bass player, or if they do, it's gotta be arranged nicely as to compliment and not compete with the other instruments, and that may be really, really tough to do if the synth player isn't listening to you and the song as a whole.
Other then that, I'd look into a fuzz/OD/Distortion pedal (take your pick of what you like best) followed by filters - filters will be your friend. A good envelope filter is probably your best bet, or maybe a wah. After that, a flanger could spice things up nicely. However, that means that you've got to convince to the synth player that you'll take up the low ends and he's got to move his left hand farther to the right!