[Schwarzeritter]

Well it depends on your climate, if you look at the factory manual ( that is if you have that still or if it is still with the car. ) You can find some basic info the factory manuals are always good
to start with. However once you start getting into modifed vehicles, or abnormal climate or blue printed motors or high milaged motors you should begin to select a oil that is best suited for your needs. Avoid mixi matching.

Because in the South of California we get days reaching 120 degrees F. I'll run a higher viscosity. One thing you don't want to do if posible is run to high a viscosity, this can place
stress on your rings etc. During the winter I tend to go with something a little lighter and I have a specific tempreture range I prefer to operate air cooled engines within.

15w50 Mobile ( as mentioned already by shadetree930 )
0w50 ENOES or their 5w40.
10w60 Castrol / RS / TWS or Castrol Classic Oils.
Motul makes a lot of great products too, they too have a 15w50.