American has already put together a few three fund portfolio suggestions for you.

 The long-term growth oriented TRICAP:

33.3% each in AMCAP, Smallcap World, EuroPacific
 

 The Asset Allocation Growth strategy called TRIAD:

33.3% each in New Perspectives, ICA, and Bond Fund of America 

For steady growth and lower volatility, you may want the "All Weather Foundation":

40% AMCAP

40% American Mutual

20% Bond Fund of America
 

Of the pre-packaged ideas I like All Weather best. I do my own three fund portfolio

 35% AMCAP
 35% CWGIX
30% CAIBX