Sound Mods
Nissan Skyline R34 GT-R (source: Juiced)
Ferrari F430 Coupe and Roadster (source: GTR2; yes, I know it sounds similar to the one from RacersHardware.de, but it isn't the exact same one. I actually modded it myself, but I bet that I used the same source as them. Also, the new version of theirs (v5) is actually noticeably different from this one - this one sounds louder in general but not as good, quality-wise. This will be fixed.)
Ferrari F40 (temporary) (source: GTR2 Lister Storm)
Ferrari 360 Stradale (source: GTR2; same case as the F430, the one from TDU: Central probably sounds similar, but I made mine before I even saw that one, and I probably used the same source. However, this one is (strangely) of higher quality than the F430 one.)

RUF RT12 plus Noble (source: NFSMW for the Porsche (which sounds great, in my opinion), some video for the Noble (which sounds less great; sounded better in the video). Added 6-12-08)
Mercedes-Benz CLK GTR (works for the VW W12 as well) (source: TDU's Maserati MC12. Added 6-26-08)
Ascari KZ1 (sources: NFSMW's BMW M5 apparently-non-used sound; GTR2 for the backfire. Added 6-26-08)
Alfa Romeo 8C Competizione (source: TDU Enzo. Added 7-31-08)
Edonis Audio (source: Trackmania; this mod is somewhat a joke and somewhat an experiment - I think it sounds weird but you're free to try it. Added 7-31-08)
Ferrari FXX, for the Enzo (source: TDU original files and GTR2. Added 7-5-09)
Honda V-TEC Inline 4 (sources: NFS Underground 2. REQUIRES DJEY'S MAGIC MAP. Added 9-7-09)

Gauge Mods
Skyline R34 - Nismo-like (Source: Nismo 350Z, Original Gauge)
Ferrari 360 Stradale (to fix the green-ness) (Source: original gauge only)
FIXED CADILLAC CIEN AND TVR T440R GAUGES (Source: CTS-V and Tuscan gauges respectively; "HUD_01" gauge for the base. Added 7-31-08)

Rim Mods
Noble M12 GTO-3R and Noble M400 (source: TDU wheels. Added 6-26-08)

Full Mod Sets
Lexus IS-F Rims, Grill, Logo & Sound (source: TDU for everything but the sound, MW for the sound. Added 7-31-08)
Ferrari 612 Scagletti Sound (Enzo), Smoked Taillights, and Darkened Rims (source: TDU for everything. Added 7-31-08. If nothing else, download this for the sound mod.)