The Trailblazer SS comes with a decent intake system although it lacks decent cold air flow and has a reducing neck down with smaller filter.
A common practice is to open up the hole behind the grill to allow more air to enter the airbox, but it's rarely of much benefit. (see here for details)
In the pictures on the left, the chambers hanging off the stock intake near the throttle body connection and also near the air filter are baffles designed to reduce noise.
As far as I am concerned there are 3 intake systems worth running excluding building your own.
- Vector MotorSports
- ADM Performance
The IEATSRT8 and Vector are similar in design with a few changes. You can see a comparison here. In my opinion the IEATSRT8 is more "refined" than the original Vector intake with its Mandrel bent tubing, airbox seal and silicone 90 degree intake elbow.
Vector has since has released a generation II intake that now has a silicone 90 elbo like the IEATSRT8 unit and a new foot/seal for the air box. (see improvements)
From a performance standpoint, the above two intakes should be identical.
The third intake is manufactured by ADM performance and includes a 100mm MAF. Its design is totally different than the other two. This is my personal favorite but in all my testing it really doesnt peform any better than the other two intakes on a "mild" bolt on motor. I would expect additional gains with trucks that have more mods like heads and cam.
This intake requires extra special tuning over the other intakes that use the factory MAF. Normally the AFR will need tweaked slightly with any intake because of different volumetric efficiency but the ADM intake with 100mm MAF needs the MAF/hz tables rescaled as well.
Click the pictures on the bottom left for comparisons.
Installed pics can be seen on each manufacturers page: