The Volant cold air intake has the best proven results from independent dyno tests. The Volant also has a box around the filter to shield the air coming in from engine heat, as well as contain some of the wheezing sounds associated with cold air intakes.
RX Performance also just released a cold air intake, which I am sure is awesome... too bad I already installed the Volant.
RX Performance makes an intake spacer called the VMAX or Ice-lator, that raises the intake manifold slightly and acts as a thermal barrier between your intake manifold and the hot ass engine... keeping your incoming air cooler, and thus, more dense.
RX Performance is in the process of making us a better throttle body for us LY7 folk... BE EXCITED!
RX Performance also makes boost-capable pistons... probably because they make forced induction kits for the LLT and LFX, both of which are very similar to the LY7, and could probably be adapted.
Not necessarily a performance upgrade, but something to certainly consider is the RX Performance oil catch can. The LY7 has a habit of drinking oil. You dont want this nasty oil being circulated into your combustion chambers, so intercept it with catch can. In a way, I guess it is a performance upgrade, because if you dont install one, oil makes it your combustion chambers and does not burn as well as gasoline, so your engine's computer reads this as lower octane fuel, and retards the timing to compensate, robbing you of power. Performance upgrades are upgrades giving you more power, this simply gives you the power your engine is supposed to make, but whatever. Most people that install the catch can take the opportunity to drill out the pathetic PCV metering tube. It has three holes, drill out the two larger ones to 7/64", clean, re-install. That easy. RX also makes a air filter oil cap to help the piss-poor PCV system breath a little better.
MACE Engineering makes high profile cams and boost capable connecting rods. I think they may also offer a forced induction system for the LY7, or maybe just its direct injection siblings, the LLT and LFX... either way, probably adaptable.
The most popular upgrades are the Volant, VMAX, catch can, drilled PCV tube, breather cap, and a good tune. Upgrades are limited, but what is out there seems to work, so at least you are not sifting through a plethora of nonsense to find what you are looking for. Give Tracy at RX Performance a call. He will tell you whats available, mild to wild, and what it will cost. Good luck, brother.