What kind of work, is the question? Word processing, photo/video processing, professional gaming?
Lenovo Thinkpad is a pretty good line of laptops, I don't think I've ever heard anything bad about them, in fact they are well-regarded as devices that will just keep on working practically forever.
How about this one?
http://shop.lenovo.com/us/en/laptops...-series/t540p/ $679 (you can spend more money while configuring it, of course).