Since I live with a straight male roommate, I have to be careful when purchasing flowers for our place, since flower arrangements can very easily make a room look too feminine. Any flower (even roses and peonies) can potentially be integrated into an "androgynous" flower arrangement-- the key is to mix these stereotypically feminine flowers with more architectural flowers or (as exemplified in some arrangement pictured here) or fresh produce.
Adding limes, artichokes, cabbage, and succulents is an easy way to incorporate masculine touches to your arrangement. If this isn't a possibility (either because of the expense, or because these items aren't available) just keep the arrangement simple-- choose multiples of one flower or leaf and ta-da the arrangement is beautiful and genderless-- hostas, calla lilies, lambs ear, hydrangeas, leucadendron, and succulents are all good choices. Try using some of these tips when hosting your next dinner party.