I bought Heizgerat Sezts H3's:
http://www.heatedseatkits.com/heatedseatkits/iheat3/index.htmlPrimarily because I heard good things about them, and they have a Canadian distribution point they ship from, so I wouldn't have to worry about getting hit with customs/import fees.
I have an 2008 Sky RL, CFSE, and I installed my kit with the switches in the centre stack. I have mine mounted basically like this:
http://www.skyroadster.com/forums/attachments/f5/21976d1202054097-seat-upgrades-foam-heaters-img_0575.jpgExcept mine are shifted more to the left and spaced closer together because my car has traction control, whereas this car is likely an 07 Sky non-turbo.
I definitely did not need extra wiring to wire mine up this way, which is basically in the centre stack in front of the shifter. I had my doubts as to whether this kit was the same kit as mine even though they are likely the same manufacturer. However, this company has 4 various kits that are very similar in description. But apparently, I definitely don't have the same kit. No biggie. I love mine.
I live in Toronto, and my car is a daily driver. I've been spoiled with heated seats in all the previous cars I've driven. I thought I could order the Sky RL CFSE with heated seats. WRONG! WTF?!? Seriously? I chalked it up to the car being a convertible/summer car. I went one winter without heated seats. After that I slapped the Heizgarat Sezts H3's in, and it has definitely been one of the best mods of many which I love. It's extended the top down season tonnes, and in the winter, it's nice that you can feel heat within 3 minutes, and pretty hot warmth by about 5-6 minutes, even in Toronto winters.
Regardless, everyone should be installing these in their cars. Basically with heated seats wiring can be a 8itch if you haven't done wiring before. Basically comfort level with stringing cable in dashes, under carpet, etc. Simple tip, take a coat hanger, open up the ends, create a simple hooked end, and use that to push wire taped to it, or to grab wire and pull. Installing the elements is scarily easy. You can get the seats out of the car with 4 nuts, 1 bolt, and 5 minutes. There's a wealth of instructional threads across the 3 major kappa boards including this one.
Well, I installed my heated seats today. I used the same location on the dash and modified/hacked the AC controls as was posted by 2WK4u. I had to extend the switches by about 40". this was definitely not an easy mod. The seat heater itself was easy to install but routing the wires under the carpet and into the dash was a real nightmare. I wound up having to take the whole dash apart. I also found out the that the previous owner must have taken the boomerang apart a few times because the majority of the clips along the top of the boomerang were missing. If anyone knows how to get these I'd appreciate it. I drove to 4 auto parts store in the area and none had anything even close. I wasted so much time driving to auto stores and extending the switch harnass that I only got the drive's seat done.
If I had to do this again, I would strongly recommend installing them on the back wall by the waterfall under the cupholder like Elff did. Boy would that have been so much easier.

I gathered information and pictures from everyone else that had installed these and compiled it all into a single document. Hope it helps, I'll be adding more pictures later after I finish my installation.
http://www.cherod.com/solstice/HowTos/HeatedSeats.htm