VW owns Audi, Seat, Skoda, Bentley, Bugatti and Lamborghini.

Nissan owns Infiniti.

Toyota owns Lexus and Daihatsu.

And there's probably way more than that.

Edit:

Even better...

BMW
-Mini
-Rolls Royce

DaimlerChrysler
-Chrysler
-Dodge
-Eagle (brand discontinued)
-Hyundai (DaimlerChrysler only owns a percentage) -Jeep
-Maybach
-Mercedes-Benz
-Mitsubishi (DaimlerChrysler only owns a percentage)
-Plymouth

Fiat
-Ferrari
-Maserati

Ford
-Aston Martin
-Jaguar
-Land Rover (recently bought from BMW)
-Lincoln
-Mazda (Ford only owns a percentage)
-Mercury
-Volvo cars

General Motors
-Buick
-Cadillac
-Chevrolet
-Daewoo
-GMC
-Hummer
-Isuzu (GM only owns a percentage)
-Oldsmobile (brand discontinued)
-Pontiac
-Saab
-Saturn
-Subaru (GM only owns a big percentage)
-Suzuki (GM only owns a small percentage)

Honda
-Acura

Hyundai
-Kia

Nissan
-Infiniti

Porsche -They do a lot of work with VW but Porsche remains its own company

Renault
-Nissan (Renault owns a percentage)

Toyota
-Lexus
-Scion

Volkswagen
-Audi
-Bentley
-Bugatti
-Lamborghini

[source]