I usually split the bass guitar into two tracks. One, the low end, gets a HPF down low, around 2 hz, and LPF around 120 hz or so. I compress the snot out of this, fast attack, slow release, pretty high ratio, maybe 4:1 to start. I sometimes put a stereo effect on this low end, like a flanger set real slow, or a stereo detune (nice for big post rock, or death-metal type things.) I'll typically duck this track with the kick, just enough so the low end stays solid.
Then, the 2nd track is the high end, so it gets a HPF at about 350 hz or so. The slope on this hpf, as well as the LPF on the 'low end' track determine how much of those warm, yet muddy frequencies survive. This track often gets some distortion or amp simulation, and gets compressed pretty hard, too, though I might use a slower attack if I want something percussive (faster release times, too, depending on the track.) I boost a little around 800hz, if it's something I want to have a lot of pick tone. I always think of those GK 800RB amps as having a lot of 800 hz, they get that Green Day 'Dookie' type bass tone.
All of this is very dependent on the track, of course. But I find breaking the bass into two tracks with different purposes helps a lot.