I used what was apparently a Cyclotricity kit to motorise my Big Dummy a couple of years ago. I used a front hub motor- except that I have installed it as a "stoke motor" (as per the Stockmonkey kit available from t'other side of the pond, using a special Stokemonkey bracket for the BD that I bought from them).
I had the motor kit from with Electric Bike Conversions- they both install kits and sell them for DIY conversions, see here:
http://www.electric-bike-conversions.co.uk/acatalog/electric-bike-kits.html The chap who runs it seems knowledgable and you can visit them- they are very accommodating. (I wanted to buy from somewhere I had recourse if things were wrong). The battery packs they do seem at the better quality end of the market. Not sure they source their current kit range from cyclotricity now though, they have fewer options on their website than when I bought a couple of years ago.
There's a range of stuff you can add to a basic kit- sensors that cut the motor at 15mph for example. I have the pedal assist sensor on the Big Dummy, it works fine- assuming you have a square taper BB it fits with no bother.
What is really good to have/install is the "motor-cut" brake levers. When stopping pedalling, the motor will stop but there's a slight delay plus some back pressure, so a flick of the brake lever cuts the motor as you start to freewheel or if you need to change a hub gear.
It is worth getting a reasonable display unit which allows different levels of input on the move. A decent kit makes installation east BUT don't assume the gubbins will all fit easily into the supplied box, you may need some fettling.
GC
