Reason #4,582 why you always, ALWAYS, ALWAYS write up some sort of contract.
Considering there is no contract, if it ever ended up in court it would just be your word against his. That being said, all work, voluntary or not, belongs to the client. Unless you are under an NDA you *can* put the work in your portfolio, but you *can't* get royalties (unless stated in contract), you *can't* use the work elsewhere (actual code is arguable, graphics are not), and you *can't* sue on any copyright grounds since he didn't steal the work from your site or something, you did *do* the work *for* him.