Intake, header, exhaust, pulley, shocks & springs or coilovers, wheels & tires, brakes...pretty much any quick bolt-on will not void your warranty (despite what the dealership tells you). In order for any of these parts to void your warranty, the dealership will have to prove that the aftermarket equipment is what caused the problem. What upgrades will do as far as voiding the warranty, is void the coverage of the particular part that is replaced (ie: if you throw on a Stromung exhuast and you get a hole in the piping, the dealership won't cover it, but you knew that). All you have to do is know your rights. Aftermarket products that you put on your car do not automatically void your entire factory warranty.
Moral of the story? Upgrade to your hearts content. As long as you don't replace the engine internals, your factory warranty will remain in tact. Hope this helps!