Here are some of the popular brands with their parent companies and subsidiaries. Some are quite shocking.
Source: Wikipedia
Feel free to add to the list. Do cite the references/source.
Toyota
Toyota owns and operates Toyota, Lexus, Scion, has a majority shareholding in Daihatsu Motors and Hino Motors as well as minority shareholdings in Fuji Heavy Industries (a manufacturer of Subaru brand cars), Isuzu Motors (the commercial truck manufacturer) and in Yamaha Motors.
Honda
Honda's line of luxury cars are branded Acura.
Nissan
Formerly marketed vehicles under the Datsun brand name. In 1989, Nissan entered an alliance with Renault S.A. of France. Infiniti is a luxury brand of Nissan.
General Motors (GM)
GM produces cars and trucks globally under the following brands: Buick, Cadillac, Chevrolet, GMC, Holden, Hummer, Opel, Pontiac, Saab, Saturn and Vauxhall. GM is the majority shareholder in GM Daewoo Auto & Technology Co. of South Korea
Ford
Ford encompasses many global brands, including Lincoln and Mercury of the US, Jaguar and Land Rover of the UK, and Volvo of Sweden. Ford also owns a one-third controlling interest in Mazda.
Chrysler
Chrysler an American automobile manufacturer that has been producing automobiles since 1925 and from 1914 under the Dodge name. From 1998 to 2007, Chrysler and its subsidiaries were part of the German based DaimlerChrysler (now Daimler AG)
Volkswagen Group
Its major subsidiaries include well-known brands like Audi, Bentley, Škoda, Lamborghini, Bugatti, SEAT and the brand Volkswagen itself. Porsche has announced it will increase its stake in Volkswagen, thus making Porsche the majority shareholder.
Daimler AG
Daimler produces cars and trucks under the brands of Mercedes-Benz, Maybach, Smart, Freightliner.
PSA Peugeot Citroën
These are sold under the Peugeot and Citroën marques.
BMW
BMW is the parent company of the MINI and Rolls-Royce car brands.