I found an interesting electric powered bicycle on the internet. It looks like a good design but it's a one of a kind project, not a kit. Check this link.
http://www.peltzer.net/ebike/
BASIC SPECS OF V1.5
Scott 24 V DC, 1 hp motor (3 hp max)
Gates Power Grip GT2 belt primary drive
1/2" steel jackshaft on custom shaft ball bearing mount - 3:1 reduction
#35 chain final drive to rear wheel - 2.77:1 reduction
8.44:1 overall gearing gives top speed of about 27 mph
2 x 12V Hawker AGM-type lead acid batteries, 13 Ah each; later replaced by B&B 12v 16Ah batteries (also AGM)
4QD "Scoota 180" speed controller - 180A with regenerative braking
24 V charger charges in 2-5 hours typically
pedal in all 18 speeds
batteries and motor removable in 10 minutes
range 15 miles on the flat depending on pedal assist
weight 85 lbs.