Since the OP mentioned getting something done free, or at least within the tools he already has, I screwed around a bit with the stock Sonar synths this evening.
A halfway decent wobble can be coaxed out of DropZone with little effort.
The key to the wobble, as others have noted, is to get a rhythmic/cyclic modulator assigned to a critical sound shaping parameter. This generally takes the form of an LFO modulating the filter frequency, but you can also modulate amplitude, filter envelope, amp envelope, etc.
It generally helps to use a filter with a steeper slope, as the effects of sweeping through the cutoff range will be more pronounced.
Subsequently modulating the rate of the LFO will take the effect up a notch. Ya know, modulate your modulator. I believe Native instruments' Massive is so popular in the dubstep world because of the ease with which you can do this. Massive allows you to create custom multi-stage envelopes that can be used for some wicked wobble effects. It also has looping envelopes that can act like LFOs. So, envelopes and LFOs can modulate each other to no end.
Anyway, If you want to give it a try with DropZone, heres one way to get there: Pick one of the preset basses. Set the filter to a 4 or 6 pole low-pass, then kick up the resonance a bit. Accentuating the cutoff frequency helps add that bit of 'wub-wub' to the sound. Pick an LFO wave with some slope to it - anything other than a pulse wave. The space between the top and bottom of the cycle is where the wobble lives, so pulse waves that jump from one extreme to the other won't work. Cycle through the wave shapes to find one you like. Crank the depth on the LFO all the way up, then adjust the frequency knob to get the speed of wobble you intend.
You can then make the effect a bit more dynamic by drawing automation in the track lane. Set automation to the LFO frequency and draw a very subtle (shallow)sine-like curve that has the effect of making the LFO frequency 'flutter'. You may also set the LFO on the Amp of Dropzone to match (or close to it) that of your filter LFO and get an interesting result.
DropZone is by no means a great synth for wobble sounds, but it can work. So too can almost any synth with assignable LFOs or envelopes (ie. most synths).
You can dress up the sound coming out of the synth by hitting it with bit-crushing or other lo-fi type effects.
I think Massive gets you to a decent wobble the fastest if you are starting from an Initialized synth patch.
If you are a dubstep fan you've probably heard of Skrillex. I understand - via interview transcript - that he uses FM8 quite a bit for wobble basses.
I've dabbled in pulling wobbles out of my DSI Mopho using the feedback loop (which can be used in an FM-like way) to pretty interesting effect.
The tools are really endless. The trick is in the technique.
Finally, I feel the need to announce that I am not a fan of Dubstep music. I think I aged out of that demographic. At only thirty-five I am starting to lose touch with what the 'kids' are listening to these days.
Holy hell there are some killer programming techniques being used by artists within the genre, though.