I am not aware of any - that is what laptops are for. However Cooler Master makes the Storm Scout case with a built in handle on top - but it kind of looks like an old 5 gallon gas can:
Maybe you could invent something a get rich. Might be a demand for something like that - maybe a could of straps that would wrap around the computer and connect to a handle on top where the straps could be synched up. You could leave it on one computer or use it for any computer you wanted to move or lug around.