Adding contributors

Here’s my site: http://spendyourpaycheck.com/

Currently I just have a simply “Share” page with three form fields, based on my theme’s template.

However, I am looking for a widget/plugin/other that would allow one page for people to submit single posts, and another page where people can apply to become contributors to the site. The first is fairly simple, but the second is where I’m getting hung up. I would like a way for people to provide their desired username, email, and password and then apply, and then as the admin I can either approve or deny them from the “Users” section. Any help is great.