I ride a bent, so this could be completely irrelevent, and your previous respondents are probably right on but...
long boy cut shorts work for me. For me, the chafing comes form the spandex parts. The shorter more girlie boy-cut shorts are no help to me as the legs roll up on them.
I buy these practically in bulk when I can find them
http://www.rei.com/product/772410

Another idea along the same line might be underwear with the chamois, then you could wear jogging shorts over them and still get what you need, but no chafing?
http://www.rei.com/product/794385