Amped Bikes is my choice, check them out.
I have put together one of the kits for my dad on a cheap garage sale bike, and it has done very well.
I would always prefer to get a bike that I like and THEN add a kit, and I would steer clear of most of the kits you see on Ebay, mainly you need to take into consideration of two things:
1 ) Durability: :madman: Fist off, the bike must be suitable for a kit. (your high dollar ultra light weight carbon frame/forks might not be a good choice
) If your going to use a front hub motor, you have to use steel forks, aluminum drop-outs and front hub motors definitely do NOT mix! :bluefrown: I prefer a rear hub motor personally, more to the install, but more efficient pushing than pulling, and you can use an aluminum frame, just have to check that yours meets the size requirements listed on any of the kit's sites. :idea:
I don't care how powerful the motor is, or how much claimed range it has, and neither will you if your breaking spokes, bending rims and breaking throttles. Many of the "good deals" are really under-built and don't forget, a GOOD motor will actually deliver the amount of watts to the rear wheel, a cheap motor will not. Also, brushless motors not only eliminate the maintenance of replacing the brushes, they are also much MUCH more efficient, not to mention VERY quiet, so a good 500 watt brushless can have better performance than a cheap 1000 Watt motor. Also, there is a huge difference depending on what kind of riding your going to do, as to what type of motor you get. If your climbing a lot of hills or pulling a trailer, geared motors are going to be most practical. If you have very little hills, and want more top end, go with a gear-less or Direct Drive (DD) motor. There are 24v kits, and 250w and smaller motors, but as long as your not restricted by law (UK, AUS and most of Europe or some states have more restrictions) get a good 36 volt 500w + motor. In the US, your restrictions are no more than 1000w of output (that's actual power at the rear wheel, not the motor size) and no more than 20 MPH with no pedaling to be allowed to use it just as any other bicycle.
IMHO, if your not planing on pedaling, get a scooter, or a motor cycle. If your just wanting to have some help getting up the hills or extending your range, then an E-Bike should be a good option for you. Some people really go hog-wild and have E-Bikes that do 40MPH+ with no pedaling, that is silly to me, why not just buy a scooter that is going to be more efficient using gas, but if your just looking for a nice gas free alternative to commute, and get some exercise in the process, I'd say try a good E-Bike kit and you will be hooked. :thumbsup:
2 ) Battery chemistry and Power: :idea: This is another deal breaker. You can have the best E-Bike kit in the world, but if you don't have the juice to get the performance you want, it's worthless. ANY E-Bike is going to be heavier than your standard bike, most hub motors are going to weigh about 15 - 20 lbs, and then you add another 15 pounds for batteries just to give you minimal performance. If you skimp on the battery, your just making a VERY heavy bike that goes slow on it's own, and after a few miles gives you a major work-out getting home. That means, you need a battery that is going to have at least 10 Amp Hours, and 36 volts. This being said, the "sweet spot" for efficiency and power to weight practicality (meaning giving enough added power to justify the added weight) your looking at 15 Amp Hours (AH) and 48v. Lots of the kits come with Sealed Lead Acid (SLA) batteries. Trust me, save your money and get a good Lithium-Ion battery or if you don't mind the potential for BBQ'n your privates :yikes: if they cook-off, get Lithium Polymer. The first battery set we had for my dad's project (three 12 volt SLA's) weighed 34lbs alone! :eekster: The SLA's seem great at first, they are cheap, easy to find but in the end, the $80 - $150+ you spend will be MUCH better off for a good Li-Ion pack that is going to weigh 30% less. After 1 year of use, the SLA's are at about 50%, and much longer and you will have to replace them, costing that same $80-$150 every other year. Many people get sticker shock because a decent battery is going to be in the $600+ range, but you get what you pay for. The Li-Ion packs will last for 2000+ charges (generally 5-7+ years) so in the end, they are cheaper. There are also Nickel Metal Hydrate batteries, which are in the middle of the road as far as weight and performance, but are only good for about 1000 charges, and cost nearly as much as the Li-Ion. Lithium Polymer are the champs when it comes to raw performance, but at the price of a short life (600-800 charges) and depending on how hard they are worked, they will be at about 50% of capacity after a year or so just like the SLA's ... oh ya and are known to fire up the BBQ if they are over-charged, over-discharged, or punctured from physical damage!!!:yikes: The latest in Li-Ion battery technology and most commonly used for E-Bikes is Lithium Iron Phosphate (LiFePO4). These batteries are going to make you the most happy IMHO, but there are several options out there, most kits can be purchased with a battery designed for them (best way to go unless you like LOTS of research and soldiering your own batts together).
There are people using over 100v and 50 AH's but there no longer bicycles, they are ultra lightweight motorcycles that have low reliability and generally tear themselves apart pushing the limits of their drive-train, not to mention they weigh in the neighborhood of 150lbs!!
Me personally, I have Fibromyalgia, and when it's acting up, I have trouble getting out of bed, much less biking 30 - 60 mile trips, so I am going for an ultra lightweight pedal assist E-Bike, I do 30 - 60 mile trips on my Nishiki now, on a good day, but I would love to have an extra boost going up the many hills here in Oregon City.
I have had really good experiences with Amped Bikes (ampedbikes.com) and the owner is a stand-up guy with a reasonably priced product.
Other people have had good experiences with E-Bikekit.com, but I can't speak from experience.
If you want a lot of E-Bike info, go Here:
http://endless-sphere.com/forums/
Look under the E-Bike section. There are people using E-Bikes for everything from commuting to MTB trail riding.