Even tho I use other methods these days, I can remeber chopping up samples for basslines and man you can make it sound almost as tight as a synth or whateva else heads are using these days. Just find some bass sounds (ie. samples) cut out a bass note you like. Dump it into your sequencer. Tune it to the rest of your piece (ie. adjust pitch by cents until it sounds like it matches), then start cutting it up. Raise the pitch of the sample by semitones to change each note (you can only change the pitch so much, too much will distort). Listen to live bass players and try to emulate their sound. Their are certain nuiances that distinguish a live sound from a synth sound. Use fades, volume levels, eqs, whateva...a little compression (not too much) also helps for a fat bass sound.
You can use this method for making your own basslines, but if you can manage it, just go and get a live player. There are tons of bass players with enough skill to lay down every hiphop bassline you are hearing these days....mostly because their made by producers that ain't musicians. Go to a music school/department and get someone to record a shit load of bass sounds and lines. I don't how useful any of this is, but there you go. Peace.