Well you gotta recognize first that most of the basses in DNB are the result of 2 or more layers - you got the sub beneath all of it creating the heart-stopping boom on the dancefloor, and then you got some middle movement things with wonky bonk resonances in the filters and that.
Filtering is always nice, when you automate the cutoff.
TAL Filter is free and sounds pretty good.
Then you can use different distortion plugins as well.
Try this on for size:
1. Make your bassline the way you think sounds nice melodically with a nice hard reece sound (google that up, reece, if you dont know how to do it or dont have good samples). Then do a sub for that, just a simple sine bass will no nicely, with the same bassline.
2. Route the signal so that you have the same sound on 2 channels (how you do this depends on the program you use, there are tutorials for it as well)
3. The first channel, put a lowpass on it at about 400Hz with just a little resonance, so that it acts as a lower layer. Also cut the the section below 100Hz from that one so it doesnt interfere with the sub. on the second channel use a 400Hz or more highpass filter.
4. On the highpassed channel put a distortion VST like
Voxengo Boogex (free) or CamelPhat and tweak until your ears hurt. Then after that put the TAL filter (with a reasonably high resonance) and set the cutoff on it so low that you cant hear the distortion anymore. After the filter, use a reverb with a nice short decay. Now when you do an automation of the TAL filter cutoff, you can emphasize the bass in places by lifting up the cutoff and letting the distortion come through. Use it sparingly tho, nobody can listen to that stuff for continuously...