I'm wondering if anyone can recommend any good kits for putting on a standard mountain bike (and links to purchase if possible and not against the forum rules). I want it to be as unnoticeable as possible. I don't mind losing some power to keep it small, but I'd like something that goes at least 20 mph and preferably 30mph without pedaling/with minimal pedaling. I've just graduated from college, so I'm ready to get out in the workplace and feel I need a bit of a step-up from regular biking, but with peak oil nearing and my green beliefs, I want something that's better for the environment and cheaper than oil.

Also, while not a strict requirement, I'd like it if the battery were rechargeable in my wall plug-in. Another preference but not strict requirement is affordablility; I'd like something under $1,000 for sure, and the cheaper the better.

So, any recommendations?