depends on what you want it to be like or represent, do you want something delicate, masculine, and/or meaningful to you? also where on the foot, the side, inside or the bridge?
delicate ones could be flowers, vines, birds, dolphin and marine like ideas, some celtic and tribal designs work too as do some scripts
more masculine could be tribal or celtic based, again some script, dragons, wolves, sharks, ships and anchors look good too.
as for personal and meaningful that depends on what you want it to mean and represent
i have several tattoos and i designed them all myself, along with ones for friends, i find if you want a tattoo you should always go for something that means or represents something or someone of important, that doesn't need to mean anything to anyone but you.