other radio button to keep at end of dynamic list of radio buttons

This completely depends on how you're currently getting your radio button options.  If it's just a manually-defined array of labels and values, for example, you would simply add an "other" option to the end. Or is it DB-backed? In that case you would simply need to append a label of "Other" to the end of the current list of labels, and decide on some value that would correspond to the "other" selection and not overlap with any of the existing ones.  If you'd like to post some sample code and/or screenshots, that would go a long way as far as helping us make some educated guesses as far as helping you figure out how to structure this correctly.