Take the cash, or a percentage of sales (get it in writing). Don't take anything less tangible than that.
The old 'trade the programmer their time in exchange for nothing' is as old as the hills and most folks around here would know better. I'd be embarrassed to offer a programmer something like that. (actually, I did offer a developer that last year but it would've been a hobby site for both of us. And I only did it because I knew them).