you don't need to go waste money and or time finding this or that vst plugin.... Majority of sub bass sounds you hear are SINE WAVES.....occasionally a sub bass comes along with some extra harmonic value that is produced by mixing a SINE wave with a Triangle, Square, or sometimes Saw wave.......
The sub bass you're looking for is probably 99% likely to just be a SINE wave played at a low tone.. ANY...and I do mean ANY synthesizer that allows you to choose your wave form, has a SINE WAVE OPTION...
If you use FL Studio, open up an instance of the 3xOsc......choose the first wave form: Sine. Turn the volume of the other 2 all the way down, and goto your piano roll and play some LOW notes....
If you use reason, its the same thing...just open an instance of Subtractive(i think its called) and choose Sine waves and play them at low notes...
If you use a program that is not FL or Reason....open up whatever Synthesizer comes with the program...and choose a Sine wave