How might I expand user information?

I’ve got my blog just the way I want it except for one last item – I would like to collect a little more information from users when they sign up. Specifically, we regularly run contests, and I’d like to do drawings for prizes from registered users.

As such, I want to create a new boolean field “enter_contest” that a user can check if they want to be included, and then a number of fields like address, date of birth, gender and other demographic information.

Is there a canonical way to add these fields to the user database and make them show up during the registration phase?

I specifically do NOT want to create a new page for contest registration. I’d like it to be part of the single account creation flow, as many people wouldn’t bother to fill out yet another form.

Many thanks!