1. The universe is very complex. (Premise)
2. Whatever is very complex most likely has an external cause. (Premise)
3. Therefore, the universe most likely has an external cause. (From 1 and 2)
The beauty of this argument is its simplicity. It very much resembles the kalam argument, with the exception that the universe does not have to be finite in the past. Whether finite or infinite in the past, it's entirely conceivable that the universe didn't have to be so astronomically complex, or complex at all. Couldn't the universe exist with a single quark? I doubt anyone in their right mind will doubt premise (1), so the key premise is (2). Since this is an inductive argument, examples will suffice. A mountain, for example, is a very complex thing, and yet we know that it is externally caused by various geological processes. Or how about the complexity of an animal? The animal only exists because of the act of procreation. I could continue, but I think enough has been said already.
Now, since the universe is the sum total of all physical space, time, matter and energy, it follows that the external cause (which most likely exists) must be timeless, changeless (for time is a measurement of change), immaterial, and very powerful in order to cause something as complex and vast as the universe. I'll leave the personality of this external cause for another time.