Subtractor is great for bass i have found. You can layer up 2 or more inside a combinator for some thick bass sounds. Try fiddling with LFO's for wobble effects. Run the combinator through a equalizer to remove unwanted higher frequencies. Perhaps boost the bass be careful not too much tho.
Of course the Thor synths offers near infinite bass sounds. But it is very comlex and needs a lot of practice to get it to do what you want.