There are a few synths that can get a great dubstep bass.

Roland Juno 60
The Juno 60 is especially useful for getting the wobble sound that so many dustup producers are seeking. The LFO can be routed to the filter. With out midi to DCB controller, we can also sync the LFO to midi clock, allowing for rhythmic, beat synced wobbles. There is a character in the filtered square wave of the Juno 60 that I recognize in many dubstep tunes.