Since most people want to have good MIDI capabilities I would look for the following models:
ddrum4 by ddrum
Roland TD-20 (replaced the TD-10)
Roland TD-12 (replaced the TD-8)
Roland TD-10
Roland TD-8
Roland TD-6
If you don't care about having a billion drumsounds, but want sounds that just sound like a killer drumkit - look for the ddrum2 or if you are lucky enough to come across one cheap (under $700 being cheap for this unit) the ddrum3. the ddrum3 has a sampler built in so you can record/sample your own sounds, which is probably not really necessary for your situation. I've seen them sell for as low as $500 and as high as $3,000 used. It all depends upon the condition of the unit, and how bad somebody wants it. Keep in mind, these last 2 units are about 15 years old, but still sell used for $500+.
They are kind of no-frills, but just have the basic drumkit sounds - no cymbal sounds in them, but they sound like a well tuned drumkit.
Like the sound on Nirvana's Nevermind CD? I've read several times that when Andy Wallace mixed it, he used a ddrum2 to replace the drum sounds that Butch Vig recorded while mixing it.
The Roland Units are great, in that they have a ton of control over the sounds, and their trigger conversion is quite fast, but not quite as fast as ddrum's, because Roland converts the signal to digital form before firing off the sound, while ddrum leaves the signal analog - so there's no conversion there to slow down the triggering process.
If you are only looking for it for Kick drum replacement, you may have another option - if you are recordi9ng on a computer, and have multiple inputs (like 16 channels to 16 tracks) on the PC, you could plug a trigger into one of those inputs, mount it on the kick, and then use one of the track replacement features on some of the drum software out there, like drumkit from hell, or Drumagogue.
It would be cheaper in the long run, and you'd have some killer drum software to use as well.
Tim