I've been looking at electic bikes for a long time. I even bought a bike with a full fairing that I was going to add an electic motor to. The problems I ran into were that:
- laws prohibit bikes from going over 35 mph
- my route to work needed me to go at least 40mph to safely keep up with traffic (even though i would be on the far right side of the road)
A problem you're likely to face is that I don't think you're going to find any electric bikes with a range of more than 25 miles. This means that you would need to take a stock bike and add additional batteries to it. There are a number of electic scooters available (which is actually more likely to be what you're looking for) that have a top speed of 30 mph, but I don't think any of them covered the range you need. Although they typically have a small storage compartment in the back, it would be a difficult task to shoe in enough extra batteries (and keep up the reliability) to achieve what you need. (I think all these I have read about run off of standard lead-acid batteries).
Ideally, someone would manufacture one of these with a mass of lithium cell-phone batteries. That would up the range to about 60 miles. With a recharge at work, that would allow you to make your commute.