What default files come with Linux shared hosting accounts?

Default site directory

welcome.html
This page serves as a placeholder until you upload site content. It lets visitors know that a website is in the works.
php5.ini
This is the PHP 5 initialization file. It can manage forms, server, and environmental variables, server-side cookies, temporary directories, error display, and error logging.
missing.html
This is the default shared hosting 404 error page. It can be replaced with a custom page.
gdform.php and webformmailer.php
These scripts are used to create a user form that emails you its contents.

webformmailer.php was added in May, 2008. For information on adding it to older accounts, see Reinstalling the Default Scripts Directory on Linux Shared Hosting.
favicon.ico
This is the icon displayed in a user's browser address bar. A blank one is provided by default.

Default scripts directory (CGI)

gdform.cgi and gdformssl.cgi
These scripts are used to create a user form that emails you its contents. gdformssl.cgi uses SSL to transmit data.