geez... not one of those again...
You want a REAL electric supercharger? Check out this URL: http://www.boosthead.com/home.php
Thomas Knight electric superchargers, they're the real deal. But be warned:
1: they aren't cheap
2: they will require tuning, just like any custom FI setup
3: batteries will be an added expense, and make for another technichal hurdle to complete the system.
He currently only sells a roots-style ESC, the centrifugal ESC will be available soon. available in 3 boost levels: 2-3 PSI Centrifugal, 5-6 PSI, and the 8-12 PSI version, he Mr. Knight reccommends you don't exceed 5 PSI on stock internals! They range in price from $795 for the low boost model to $1795 for the high-boost centrifugal (almost $2000 for the roots-style high-boost model)
Since we can't easily get high-output alternators for our cars, you will either need to run 3 standard car batteries (to recharge off the alternator) or run 3 MIL-spec batteries (which will have the same weight of a single car battery, but cannot be charged off the stock alternator, you will need to hook it up to a battery charger when not in use)
It has it's drawbacks, but it is the ONLY viable electric supercharger available that actually works. Everything else is BS.
Thomas Knight, the guy who invented this thing, has been in legal battles over other companies regarding his invention for years. He only now has won the right to market the things. Before making these for public sale, he made custom turbo and SC setups for a variety of cars, I know people who ran his kits on the escort back in the day, and they were high-quality. so Thomas knows his stuff.
Definitely worth looking into if there isn't a turbo or SC available for your car. Battery weight is a drawback though. Think of it like an electronic nitrous kit, it'll boost at wide-open throttle, as long as your batteries have juice.
His site goes into a lot more detail regarding the technichal aspects you need to consider; it's well worth a look. Below is a pic of the Roots-style unit;
Oh, in case you still think it's BS, check out this article from Turbo magazine reviewing the ESC:http://www.turbomagazine.com/tech/0406tur_knight/