My top ten would be:
Land Rover (Defender) United Kingdom
Ariel (Atom) United Kingdom
Caterham (all) United Kingdom
Koenigsegg (CCX) Sweden
Spyker (C8 Aileron) Netherlands
Gumpert (Apollo) Germany
HSV (Maloo) Australia
KTM (X-Bow) Austria
Joss (JT1) Australia
Radical (SR8) United Kingdom
Your doesn't have to be top 10 just list some of your favorite brands.
The only one I haven't heard of from this list is the Joss JT1 and no I don't play Forza and I started and stopped playing Gran Turismo with 3. The majority of my car knowledge is gained from Top Gear(the original, not the Australian or the, shudder, American).
My favourites are:
BMW(M5, M3 or 1M)(earlier models, before the ugliness)
Morgan(4/4, Aero 8 or Supersport)
Koenigsegg(CCX)
Mercedes(SLR or SLS)
Range Rover(same with BMW)
Fiat(500 Abarth)
Noble(M600)
Ferrari(F40, F355)
Aston Martin(DB9)
Maserati(Quattroporte GTS)
Bugatti(Veyron/Spersport)