What kind of list do you want? You can always run a query on the database using phpmyadmin:
Code:
SELECT user_id, username
FROM xf_user
WHERE gender = 'male';
Code:
SELECT user_id, username
FROM xf_user
WHERE gender = 'female';
If you want to save the results then click
Export at the bottom of the page in phpmyadmin after you run the query.