Geweb

Use this plugin if you want allow users create their own sites based on your.
<h3>Arbitrary section</h3>
You can create your own HTML code of the form. 
Create file in your theme, put code from plugins/wp-auto-mu/geweb-mu/register.php to your new file and add_filter geweb-mu-register-path to rewrite file paht for the form.

WPMU User own site

Plugin allows to create site on user registration in WPMU environment.

Kezz Bracey

This is a simple plugin that adds plugin & theme add & manage shortcut links to the admin bar for Multisite managers.
I’m constantly adding, removing and otherwise managing plugins and themes on my WP Multisite networks. I personally found it tiresome to click through to the plugin and theme management area of my network admin as often as I do, and wanted to speed up the process.
This plugin adds four links to the admin bar as a drop down, allowing 1 click access to add & manage network plugins & themes from anywhere in your network.
NOTE: Only super admins will see these shortcuts.

MU Admin Bar Shortcuts

This is a simple plugin that adds plugin & theme add & manage shortcut links to the admin bar for Multisite managers.

WPMU User own site vs MU Admin Bar Shortcuts