As part of our work on Discourse 1.4 I spent some time enhancing user fields:
One of our most requested featured for user fields was dropdowns, so now you can add them. The options can even be dragged and dropped for reordering!
For some users it was very important to display the fields in a particular order. In the latest Discourse builds, you can reorder the fields. Just use the up and down arrow buttons, and the fields will be displayed in the same order when the user signs up.