Depends what your budget is mate The classic synth for big bad bass is the Access Virus, but it is quite expensive The MicroKorg or MS2000 might be worth investigating In terms of VST's i'd look at Albino, Z3ta+, Moog Modular. Personally i've never come across one soft-synth that has been able to make tearing bass sounds right out of the box but once you sample the synth and give it some distortion and effects then any of those synths are worth looking into