I agree with Quazar. I had never heard of Kv, and kV was freaking me out thinking about 3000 kilovolts!

Hey, just a nit here, but you should change "kV" to "Kv". Have a look at this wikipedia entry: <http://en.wikipedia.org/wiki/Brushless_DC_electric_motor#Kv_rating>
You wouldn't want somebody to try to run 3000kV through one of these ;)
- Dean

ARE you guys getting more of these?

It would be nice to find a Datasheet on this motor and the 4300Kv version as well, as we know the Kv rating, but what is it's base speed? Maximum values etc. I've been searching everywhere for something on them but with no real luck at all

Could someone tell me how to determine the torque this thing gives?

Final Point...
4.) Atmel (same microcontrollers as on Arduino) have really, really well documented Application notes and theory explanation on their website for Brushless DC motor control. Particularly Sensorless control. Google the following: "AVR 928 filetype:pdf" and do the same for: AVR 172, AVR 194, AVR 444 and AVR 498.
I hope this answers the Hall Sensor Comment...these motors are controlled off Back EMF from the motor windings and dont need hall sensors...

3.) Direction control of the Motor depends on the ESC model. If it is reversible, you can implement both forward and reverse by adjusting the PWM duty cycle to the ESC. NOTE: You have to ensure that you run through the PWM range when changing direction, as it would be done if you were holding an RC trigger in your hand!!!! If you just change from, say 1ms to 2ms directly, you will change from full forward to full reverse current and voltage instantaneously. If you have a 35A ESC, this will result in over 70A which will fry all of your components, motor and ESC...so be careful!!

2.) If you don't want to pay for the Programming Card, you can program the ESC by mimicing the manual setup routine which is accomplished through pulling and pushing the trigger on an RC Remote through the throttle range. IE: send the ESC the required signal for say, full throttle (2ms@50Hz. You get the idea? Manual programming routines can easily be found in online RC forums. You can also write a bit of code to talk to an arduino over I2C and create hyperterminal commands such as "set speed" which the micro then translates into the required PWM throttle signals. (Easier than you would think) But I still say...just buy the programming card.

I have a few points to add here...
1.) I have been staring at this stuff for a while. I have a degree in Mechanical Engineering and a second degree in Electronic Engineering. If you want to save yourselves the maximum amount of implementation time, the products on this page are best value that you will find. Dont waste your time and money on e-bay. It is a nightmare programming those outdated ESCs at circa ?1-5. This is simple...buy the ESC, buy the motor, buy a programming card (once off) and the only interface which you need to the microcontroller is a PWM signal to mimic the throttle signal from an RC remote control. Typically, "The ESC accepts a nominal 50 Hz PWM servo input signal whose pulse width varies from 1 ms to 2 ms. When supplied with a 1 ms width pulse at 50 Hz, the ESC responds by turning off the DC motor attached to its output. A 1.5 ms pulse-width input signal results in a 50% duty cycle output signal that drives the motor at approximately half-speed. When presented with 2.0 ms input signal, the motor runs at full speed due to the 100% duty cycle (on constantly) output."
http://en.wikipedia.org/wiki/Electronic_speed_control

the kv refers to K sub v http://en.wikipedia.org/wiki/KV this represents rpms pre volt not kilovolts

Uhh, throwing in my two cents in hopes for some sparkfun representative feedback... uhh, a bit curious about this, these brushless motors would take the equivalent of a laser power supply (extremely high voltage) to run at their rated voltage.. which i find rather odd. I run regular brushless motors quite often (tri-pole bridge brushless motors, just like these ones) at 12 volts (the rating on my motor) and it works just fine. since when has 36 gauge magnet wire been able to have 3 kilovolts run through it without internal arcing? just wondering. by the way, if you find any large lots of harddrives being sold on the cheap, you can source LOTS of these out of those old 5-10 gig harddrives that will easily run up to 10k rpm and have fluid bearings... but i digress. i'm guessing the specs were misread on this one or something.. i just have some extreme disbelief that these would take 3 kilovolts without some serious enamel wire melt-action...

Could you guys post some specs on this? Voltage rating and rated speed if you have it.
Line-to-line resistance and inductance would be nice if you can measure it.

Huge kV rating! If you want a robot that goes 80mph, then this is your choice.
Needs gearbox, me thinks. At 3.7V it runs 11.000rpm which is "quite" fast..

someone knows how to interface this stuff with a normal microcontroller?
I mean, I got a bunch of "speling explanation" and not a very clear one... I see a bunch of three phases and everything stuff but, nothing that really cleared my mind :S
maybe I'm a dummy guy, probably, so someone knows or can make a brushless motor for dummies?