Since the biggest thing holding electric cars back is battery technology, EV converters need to be careful in how they use the power they have. As a result many EV converters avoid having air-conditioning since the power draw has a noticeable effect on range, others decide the small sacrifice in range is worth it for the increase in comfort. Here are several options for keeping the occupants of your EV cool and comfortable:

• No Air-Conditioning: Air-con uses the same amount of power in an ICE car or a EV it is just less obvious in a normal car. Once the drain of air-con is realised many people decide that having the window open or using the fan alone are sufficient enough cooling for them. If range is a big priority and the temperatures of your area don't get excessively hot then this is the simplest and best option.
• Dual Shaft Motor: If having AC is a must for your conversion then the option that is most similar to AC in a normal car is to run the AC compressor off the rear shaft of a dual shaft motor. The advantages are simplicity and similarity to standard cars but the AC will only work when the motor is spinning. This Saab is an example of using this approach.
• Accessory Motor: Another option is to run a small 12V accessory motor which is attached to the compressor. This approach allows AC to be used when the car is stationary and means that there is no direct drain on the power to the drive motor but adds weight and complexity. This Honda is an example of using this approach.
• Ice: Rather than storing electricity and using it to lower the temperature of the car it may be easier and cheaper to store a direct source of cooling; ice. Blowing air through an ice water mix is a rather effective form of cooling and might be sufficient for your cooling requirements. A DIY example can be seen here, or you may prefer Mr Sharkey's no nonsense approach here.
• Compressor with integral motor: A more recent option is a compressor with a motor built in like your home AC unit. Some of the newer hybrids use this technology such as the Prius or this conversion which utilizes a variable speed control to maximize efficiency. With this option you also have more freedom as to where to locate the unit and you don't have a lot of mounting hardware to fabricate. http://www.evdrive.com/BMW_project/AirConditioning.html Extension of the above is DC powered complete unit. Expensive , but compact. DC-Breeze is an example. ~$2,500 for 5,000 BTU / hr cooling all in a ~50 pound package... just plan for the ~580 Watt load to run it.