Frank's Xipi kits are more or less plug and play if your budget stretches that far. The Ezee kits are also very good and quite powerful. The motor is very strong and can give a lot more than what the standard kit's set for. Maybe if you called Cyclezee on the phone, he can help you with a bit more torque. I know the Americans have the same kit set to 20mph and much higher current. Next is the Oxygen kit. I have one myself and it was easy to fit. I wrote a review thread about it somewhere and so did Geoff9 if you do a search. The Oxydrive speed limit can be reset to 24 mph via settings in the display; which is great on the flat with a following wind, but don't expect it to power up hills at that speed. It's still only a 250w motor, so will slow down on hills and into strong winds, but it'll out-power your average 250w Chinese bike.
One last thing: Kudos tried a bottle battery on a carbon framed bike and had problems with the studs pulling out. It can be done, but not by simply bolting your battery to the bottle fixings. You'd need to do a bit of reinforcing.