@pablo - I've already run through that tutorial, thanks. Like I said, the WP files are download, in the correct directory, with the correct permissions (user and group are both the nginx user), the wp-config.php file and setup correctly, the database is created, and the site is displaying. The only issue is I can't actually log into the Dashboard and administrate the site through the GUI. I can see the files through SFTP and I can administrate the site through the command line (usiing WP-CLI), but I can't log into the site by going to the login page.
@Ben - Normally, when you go to the wp-login page, enter your credentials, and hit the Submit button, the page refreshes and you're sent to the Dashboard. In my case, I get sent back to the login with no errors. The URL changes from http://christopherjoel.com/wp-login.php to http://christopherjoel.com/wp-login.php?redirect_to=http%3A%2F%2Fchristopherjoel.com%2Fwp-admin%2Fprofile.php&reauth=1. On other servers (like my current web host - not at Digital Ocean), this page then redirects to http://christopherjoel.com/wp-admin/. So, its trying to redirect to the Dashboard, but for some reason, it doesn't. Is that more clear?