There are numerous choices for intakes, exhausts, and a few for the header. As for suspension parts, you have numerous springs and bars to choose from. The only thing that's really lacking right now is the replacement shocks. Only Koni has released their shocks, but the front are just inserts. But you could get coilovers instead.

Let's not forget the Hondata upgrade, which I suppose is meaningless right now if you're running nitrous, but if you're running NA, it's a must-buy.

What is it exactly you're looking for? Based on what you wrote, I'm going to assume that you're looking to go FI. In that respect, then you're right, the turbo aftermarket for the RSX isn't big at all. I think there's only 2 available kits available right now: Cybernation and Revhard. But in due time...