If reliability is a key consideration, I don't know how you could do better than the Panasonic system that AllenG mentioned. Bikes with Panasonic systems have been available in Europe for the better part of 10 years and have a legendary reputation for reliability. (I find it wildly ironic that European bikes are using Japanese motors). I believe the Panny system was available in the United States on Giant bikes until 2006. This year it's become available again in the US on Kalkhoff bikes imported from Germany. (Does anybody know if any other manufacturer is importing bikes with Panny systems into the US?)
Regarding other criteria:
It's a pedal assist, no throttle to speak of.
It's an exceptional hill climber. The motor connects directly to the chain, so is able to utilize the low gears of derailuer / gearing system. I believe Optibike and Kalkhoff were the only ebikes that made it to the top of Pikes Peak last week.
Starts at around $2500, more than an Izip, less than an Opti.
Looks and behaves pretty much like a conventional bike, with the battery behind the seat post giving it a longer wheelbase.
miro13car's right: reliable = $$$