I had some spare time and an old Pintech trigger that was attached to my brother's drums when he got them (I thought it was broken, but figured "what the hell")
Anyway, I tried recording the direct audio spikes from the trigger and converting it with Drumagog. It worked 100%. Here's a brief explanation of what I did and the results:
I duct taped the trigger to the beater head of the bass drum (very ghetto.) I would suggest finding a nicer looking way to attach it. It would have worked fine on the other side as well, I'm sure.
I used an old version of this trigger:
http://www.musiciansfriend.com/srs7/g=home/search/detail/base_pid/444893/
so you can do this for under $20 now (minus the cost of drumagog.)
I used a 1/4" instrument cable to go directly into my recording hardware. Make sure to keep your input levels low, no sense in damaging the inputs. I checked my levels and began to record.
This trigger is a bit microphonic. If you listen closely to the raw track you can hear the other drums that I hit, but the nasty sounding signal the kick is much louder. Mind you, I'm no drummer, so I just played simply. The pattern is kick kick kick (mid tom) kick kick kick (floor tom) kick kick kick (snare).
here is the raw track, amplified to bring up its overall level and with no other processing:
Next I loaded the resulting mono track in a freeware multitracker that supports vst plugins called kristal audio engine. (Actually before I did that I amplified the raw track a little so it would be easier to work with, but didn't gate it or anything else.) I loaded drumagog as an effect for the channel and just hit play. With the default settings it worked perfectly. Well, it played as a snare until I changed it to a kick, but you know... The direct recorded track was too quiet to track properly without some tweaking, but the amplified track that I used as my "raw" source (remember, no other processing) worked like a dream. The software had no trouble distinguishing between the kick and the other quiet but clearly audible drums.
Finally, I exported a stereo mixdown so you could hear the result. This uses the Ludwig sample that Fairview posted (Thanks Fairview)
Here is the result:
In conclusion, it works perfectly. For a very small investment in hardware and the price of the drumagog software (free if you only need it for one project more if you want it for ever) you can get great sounding kick drums. It probably works fine on snare as well, and maybe later I'll experiment with toms. It doesn't take any time to learn or implement. I got it right on the first try, and I'm no engineer. Everyone anyone that has a track to devote to the kick drum should try this.
If I have time later I'll try to get it to work the same with the free plugins that people have posted.
Finally, I did try hitting the kick with varying force to test for dynamics, using Fairview's gog file. Drumagog seemed to handle dynamics fine for those that are looking for it. If you don't want dynamics, just compress your track severely and tweak to make sure no other noises trigger drumagog.
PS - sorry for the novel. I hope people found it informative.
Edit:
DrumTrig (
http://www.stormrecordingstudio.co.uk/VST.htm) also works. This one is free, and uses any wav sample. It doesn't allow for dynamics like drumagog does, which is probably good if you're a sloppy drummer.

Be sure to bring the retrigger option down quite a bit. At its default it's too slow even for the slow sample that I posted above.