I'm going to guess that based on the responses you have received so far you understand that whatever you need to adequately secure your bike is going to be heavy and bulky. It is the price we pay for security. A nice chain with a good mini-ulock is about the minimum you should consider if you want very good piece of mind.

I will sometimes use a heavy cable with the locking mechanism build into it to secure my ride for the day at the train station, but I would not use that for one of my more expensive bikes - even in the relatively low crime area that I lock up in.