So, you're looking for an electric assist bike because your bike is horrible and no fun to ride. Well, before you plunge in, let me advise you at no cost.
1. The electric bike market is hot, so there are people literally coming out of the woodwork to sell you an electric bike. Many, if not most, of these people have no experience with bikes in the first place. From the manufacturers in China to the guy selling them out of his hardware store they new to this so what I usually see is oddball geometries, crazy setups, amateur assemblies, and torturous position and fit. A bike's geometry affects everything and adding a heavy motor to a bike that didn't ride well to begin with is bound to end in tears.
2. Slapping a motor on a cheap bike and selling it for $1500 is a great deal if you're the one selling the bike. However, low-end bikes have low-end parts and these parts cannot even withstand gentle use let alone the speeds and forces associated with a motor. When you wind that super-heavy bike up to 25mph with brakes that cannot even stop a normal bike at 15mph you may find yourself in a spot of bother before long.
3. I've worked on low-end electric bikes for 7 years now. I can assure you that it's not going to be a happy experience either for you or for the mechanic. I no longer work on them due to my insurance company explaining to me the risks associated with them. Also, my repair stand and my back aren't sufficient for a 60lb monster.
4. When your bike does fail, there isn't anywhere for me or for most bike shops to obtain parts since the companies selling these gems aren't supported by the normal bike supply chain (QBP, JandB, NACycles, Cyclone, United, etc.).
5. A real electric bike, if you're set on buying one, should come from a BIKE SHOP. Since I have no formal training in electric bike trouble-shooting and repair I don't sell them. However, if you can find a local shop here in town who has a certified mechanic on staff who has been through the workshop on whichever drive system your bike has, then you're probably fine if your problems come close to home. If you're in Cody, Wyoming on vacation...probably not. I know KHS, Haro, etc. have proven and supported drive systems and many other brands do, as well.
6. Lastly, if you aren't prepared to thumb over $2500 for a real electric bike, I might suggest something fun to ride and super light and under $800 and custom made for you. Check out Rollbicycles.com