I'm not going to talk on the SS, you should know all about those from by now.
The WRX is a nice looking car. Decently fast and AWD is a major plus. Good aftermarket, and plenty of tuners out there for it. Only thing I could see bad it that is might be expensive if anything goes wrong on it.
The Acura RSX...if you get one get a type S. Don't settle for anything less, or you will be in for a big disappointment. Fun to drive when you finally, after a long and painfully slow run up to the powerband (i.e vtec), make it to the upper ranges of the RPM. Has a 8000 RPM redline. Suspension is good, but on the soft side. Has very noticeable body roll. Stiffer springs will make up for that though. If you can find one for the right price, I would go with it, but this is if you absolutely have to get out of a Cobalt.
The pontiac G5 Gt...isn't that just a different Cobalt SS/NA? Why bother.
Don't know much about the other two to comment.