The Perfect Laptop/Gadget Bag?

I’ve been lugging my laptops and assorted gadgets around half the globe in a variety of bags — from too heavy backpacks and Dell bags (providing good protection, but almost heavier than the laptop itself) to flimsy conference give-away bags, nothing seemed right.The ideal laptop bag to me must be within the limits for cabin luggage, spacious inside, lightweight, robust, and provide some reasonable protection to the electronics stored in it. Where do I get it?