What turbo or supercharger kits will work best with my 2.4l engine?

Check out ZZ Performance. They will likely have what you need and are reputable and knowledgeable if you have questions. Having said that, if you want a supercharged/turbocharged Cobalt why not just buy one? Building your own is grossly expensive. It's a lot more than just bolting on a supercharger. The GM engineers can do a much better job than you ever can and then you can build on what they've already done if you want more instead of having to reinvent the wheel first.