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.

It was a harmless nonvenomous Diamondback Water Snake (Nerodia rhombifer). Diamondback Water Snakes are one of many nonvenomous water snake species and are not at all related to the Western Diamondback Rattlesnake (which is venomous) or the Western Cottonmouth (the venomous snake commonly referred to as a "water moccasin."). There isn't much you can do to deter snakes other than remove their habitat (which usually isn't practical or desirable). There are lots of urban legends about the deterrent value of mothballs, lime, sulfur, etc. but none of these products deter snakes. Neither does a product called Snake-A-Way which should really be called Dollar-A-Way because it separates people from their money rather than from snakes. The good news is that the snake species is nonvenomous and poses no danger to pets and small children.