Parts suppliers I've used can be found on the Parts page.
Here's a list of other automotive websites of note, in no particular order:

NSX Prime NSX Trader Online RealTime Racing
NSX Files Ultimate NSX Reference Procar Specials
King Motorsports StopTech Acura Club
Viper Club of America Auto Salon Auto Sales V8 Supercars
McLaren Cars LTD McLaren Photo Gallery AARRF Club Racing
Race Deck Flooring Longacre Racing Products Acura NSX-R 2002 Page
Classic Car Collection Honda Tuning Magazine Autosport
Racecare UK Danoland Goodwood Estate
Comptech F1-Live NSX Registry
Holman Moody GT-40 UK Site Porsche 917 LMK
Ultima Cars UK Barchetta Classic Bridgestone Motorsports
Mosler Automotive Taitec / GT-ROM Japan Site HANS Device
Diversified Cryogenics Slowpokes Drivers School FastVoice NSX
NSX God EXP4 Performance Additives