ok here's the list

header: Comptech race header, JR race header (i have this and let me tell you race header's gain is very good on this car, if u only have money to buy either header or exhaust, get race header)

exhaust: Fujitsubo Powergetter (better sound), Fujitsubo RM01 (better gain), Amuse R1 titanium, 5Zigen Fireball (i have this, it's quiet and decent gain), Spoon N1 (sounds good but look ugly)

Wing: i think the Type R wing is the best, nothing fancy nothing too exaggerated, many of us uses type R wing replica. (authentic honda R wing will cost u $600 or so)

body kit: well i m not very into it but i think the original R lips, Mugen, INGS kit are very nice. the worst i seen is some cheap AirForce thing, pls don't get it.

suspension:
- Springs -
i don't think you are into road course or auto x style ... but i think cornering ability is a quality that you can't miss when you are purchasing a suspension part. so, my suggestion is eibach Sportsline springs (I uses pro kit, but to u it prob doesn't have enough drop) which get you a decent drop, Prodrive
and Progress also have pretty good springs. Eibach has camber kits so no prob there.

- strut bars -
well the strut bars doesn't do much on this car, u can try cusco, spoon (i use spoon but i can tell you it doesn't do jack), mugen bars, they are all pretty good quality.

- sway bars & X brace -
if u are into cornering, this is what u wanna get to improve rsx-s. I believe eibach just came out new sway bars for rsx-s and it should be nice. I have Progress sway, which i'd highly recommend. besides them mugen i heard is very good too. now X brace i know neuspeed has one and my friend had it for long time, he said it strength the lower body and u can really feel it, and best thing is x brace is easy to install and cheap!


last thing... since u are into mods, i suggest you also get the Hondata reflash, you can't go wrong with this mod!