I started a bass thread here a couple weeks ago, there was some good info in it...you can probably still find it.
I was completely unsatisfied with my bass tone, but now that I've really put a lot of effort into it...I've never been happier.
First of all make sure that your bass has brand new strings, dead strings sound like utter shit. Then make sure that you have good string to string volume. Your low E shouldn't be louder than your A string, etc.
Ultimately you're going to have two bass tracks. Record a dry DI track, no distortion, and also record a distorted amp track. Low pass the DI track so it slopes off at like 400Hz. High pass the distorted track so it slopes off at 650Hz or so. Drop your favorite EQ on the DI track and tweak the lows so that it best fits with your kicks and guitars. Need to compress? Probably. Buss the two tracks together and compress them together, or you can compress each differently with a compresser on each individual track.
During mixing, set your levels for guitars and drums first, then bring up the DI track till the low end fills out how you want it to. Now for the fun part. Bring up the high passed distorted track till you can hear the bass growling along with the guitars. I really, really like to hear a heavily distorted bass...it just adds that extra ounce of aggression.
Basically the whole reasoning behind this is that you're getting a big rumbling distorted tone without distorting the low end. The smooth undistorted low end will fit in the mix much better than a sloppy overdriven one. You can also bring up the high-passed track and get the bass HEARD without messing with the low end.
