Plugins that add new fields to registration and user pages:

http://wordpress.org/extend/plugins/pie-register/

If Pie Register does not seem to create your fields its because there is a bug with some browsers or OSs that makes the name of the field appear after the options field (see screenshot). It works fine if you enter the name of the field in the second input field.

http://wordpress.org/extend/plugins/cimy-user-extra-fields/

Removing Unnecessary fields from the user profile

You can remove the colour scheme on the user profile via the following code:

function admin_del_options() {
   global $_wp_admin_css_colors;
   $_wp_admin_css_colors = 0;
}

add_action('admin_head', 'admin_del_options');

If you want to remove the Aim, Jabber and Yim fields you can also use this code:

function remove_contactmethods( $contactmethods ) {
  unset($contactmethods['aim']);
  unset($contactmethods['jabber']);
  unset($contactmethods['yim']);
  return $contactmethods;
}
add_filter('user_contactmethods','remove_contactmethods',10,1);

Only adding fields to the user profile page:

http://bavotasan.com/tutorials/adding-extra-fields-to-the-wordpress-user-profile/

http://justintadlock.com/archives/2009/09/10/adding-and-using-custom-user-profile-fields