apriorit

This plugin allows you to more conveniently manage the creation of multiple sites within a multisite. 
Now you can create subsites and their pages with just one click.

Site Generator

This plugin allows managing creating multiple sites within a multisite more conveniently.

OzTheGreat

For WordPress Multisite (WPMU) installs, allows Super Admins to easily manage each users roles and blogs from one 
screen in the Network Admin menu.
You no longer have to go to each blog to change the user’s role. It’s also 
much easier to see which sites a user is associated with.

Multisite User Role Manager

Ajax management makes it super easy to add users to a bunch of sites in the network. Does 1 things really well, more plugins should work like this.

Great for multisite user management

Made adding a user to 20 sites a lot easier than using WP's default interface for that (way less clicking around).

Much easier to assign a user to many sites

I spent about 30 minutes looking at different multisite user management plugins and all of them were either out of date, or tried to do too much. This plugin solved the exact issue I was dealing with: adding a user (with a specified role) to all of my client's subsites. 

Thank you very much. 

I wish you all the best,
Kevin.

P.S. the CSS for the admin screen where you add users to subsites was a bit off for me (in Chrome). The table did not fit the modal background (it hung off to the right a bit, and forced me to scroll even though there was plenty of vertical space). It doesn't bother me but it might bother some other users so I figured I would let you know. 

Excellent plugin - it does what it says!

Manage user roles for each blog from a single screen on multisite (WPMU) setups

Site Generator vs Multisite User Role Manager