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