Forums:

NSXPrime.com (The top forum for NSX)
CorvetteForum.com (Major corvette forum, useful info and mature members)
SupraForums.com (The best forum for any generation Supra)
240sxForums.com (Great forum dealing in the s13/s14 240sx only)
Nicoclub.com (The best all Nissan/Infiniti forum I've been a part of)
Bimmerforums.com (As far as I have seen, this is the best BMW forum on the web)
Team-Integra.net (If you have any generation Integra, this is the place for you)
Honda-Tech.com (Hands down, the most intelligent Honda/Acura forum in existence)

Technical Information :

Mkiv.com (Technical articles, how to's, and more for the Toyota Supra)
Supra Hardtop Registry (Features statistics & owner's profiles of the rare 93-95 Supra Hardtop TT)
Meggala.com (Technical articles, how to's, and more fot the Nissan Skyline and RB motors)
Importnut.net (Detailed info and how to on 300zx brake swap for the 240sx)
GA Tint Law (New Georgia Tint law information)
RB30DET Build (Detailed guide on how to build the awesome RB"30"DET frankenstein motor)
NISSAN FAST (FAST program which allows you to crossreference any Nissan/Skyline part)
FAST Instructions (How to download the Nissan FAST program. You need a BitTorrent)
Honda Shop Manuals (Free downloadable shopmanuals for Honda cars)
E36 BMW How To's (A hefty collection of E36 BMW how to guides)

Calculators:

Tire Size Calculator (This will tell you speedometer changes with different size tires)
Gearing (A spreadsheet that lets you calculate speed at different gear ratios and revs)

Vendors:

Horsepowerfreaks.com (They carry tons of aftermarket parts at good prices)
MVPmotorsports.com (Excellent source for Supra parts and JDM aftermarket products)
TireRack.com (Always the best prices on tires. Quick shipping. I have used them many times)
DriveShaftShop.com (Great custom driveshafts at a reasonable price and quick shipping)
CosmosRacing.com (Awesome E36 M3 intakes, priced well below the major competitors)