GM purchased lotus in the 80s but they sold it to a malaysian company some years later, they just have a contract with lotus to build vx220 and opel speedster. Apparently, the contract is going to expire this or next year. GM does own 20% or so of subaru's parent company. That's why there's the partnership between subaru and saab in making the new wrx based saab 9-2X.
To add to the list, GM owns part of Fiat and Delta motor, a south african company. I believe GM also owns lada (or whatever its parent company) as well as daewoo.
On the electric cars side, Ford owns Think while GM and chrysler own ballard power (fuel cell)
Daimler chrysler have control over mitsubishi, they took over the management over the recall scandal.
Obviously we have to add BMW to the list, they own Rolls Royce and Mini
To complicate things more, we probably have to add all the chinese car companies into the list. GM and VAG put considerable amount of investment there.