Before I make a recommendation, I would want to know if you need a rear rack on your bike for carrying things, what conditions you expect to ride it in, and whether there's any laws against eBikes in your location. Also, do you have a bike already that would be suitable to add an eBike kit onto? Finally, how far do you need to go on this thing? Be careful about your decision on the last one. Maybe right now you just want to commute with it, but you might decide later on that you can sell your car and go everywhere with the damn thing, meaning you'll need a bigger battery, or the capability/willingness to bring your charger with you.
I personally like to deal with Lunacycle, because their HQ is in North America. Depending on the answers to the questions above, I would recommend any of the following from them:
1. Pre-Built Hard Tail Mountain Bike
2. Pre-Built Full Suspension Mountain Bike
3. Pre-Built Fat Bike
4. BBSHD Kit + Battery to add onto your existing bike
I should add a caveat to this in that I'm not sure I would recommend any DIY-ish eBike if you're not a little bit handy. Things can break and you'll have to be able to at the very least remove parts for replacement, as well as perhaps a bit of troubleshooting. Bike shops sometimes will be unwilling to help you.
Join us at /r/eBikes. We're a bit more inviting to newbies than Endless Sphere.
edit: As for worrying about theft, my condo insurance covers my eBike! $500 deductable. My annual premium is only $230 for condo insurance. Knowing it's only $500 to replace my eBike takes a bit of worry out of locking it up, though I rarely lock it in places I am worried about it.