I have an '05 Cobalt (base model) and it's almost time to change the coolant. I wanted to do it before winter.

Anyhow, I bought 2 gallons of coolant and got under the car to drain the radiator, but I can't find any sort of drain plug or valve! I searched this forum and the internet, but didn't really find anything helpful.

I was also thinking I could just disconnect the lower radiator hose, but that would be really messy. Also, it's a PITA to get at.

Anyone know where a drain valve is?

Well, I found it.

There's a small black plastic petcock on the bottom corner of the passenger side of the radiator. It's facing toward the rear of the car. I had to take off my air intake to get to it, and it was pretty hard to unscrew. The antifreeze comes out of a little hole in the rubber bushing where the radiator mounts to the chassis. Almost a gallon of coolant came out.

And I have to say, if you plan on doing this yourself:
1) Do it when the engine is cool, or you'll burn yourself.
2) Don't leave the coolant somewhere your kids/pets/self could drink. It's poisonous!