True, it may be a rat snake, but... do rat snakes rattle the end of their tails like a rattler would? That's what really threw me (after I thought about it). I mean... do ALL snakes do that when aggrivated? O.o?

It's not a copperhead. Pit vipers (all poisonous snakes in the US but the coral snake) have slitted pupils like a cats. Yours one definitely has round pupils. And you're right that it's not shaped correctly to be a copperhead. Just think of all the crickets that little beauty was eating in your garage! Try the reptile/amphibian forum if no one here can identify it. Here is a link that might be useful: Reptile forum

That is a Texas Ratsnake (Pantherophis obsoletus). They are one of the more commonly seen snakes in the eastern half of the state and into central Texas. They are harmless predators of rodents and birds.

Very gravid(pregnant) and harmless female Northern Water Snake(Nerodia sipedon). These feed on fish and amphibians and are harmless, although if grabbed or handled roughly, they will bite in self-defense and spray foul-smelling musk. She is probably seeking a sheltered spot to give birth, since she looks like she's about to explode! I keep and breed several species of Nerodia, including these, as pets, and they tame down very quickly if handled gently. You have nothing to worry about from this girl.