DeannaS

kgraeme

When users are first created, they are automatically assigned to the primary blog. But, you may want to set them up on multiple blogs by default. This is especially helpful if you’re using bbpress or other forum software where the user needs a role on that blog in order to participate. This plugin allows site admins to set the default role on as many blogs as desired for all new users.

WPMU Default User Role

Lets site admins define which blogs a user should automatically become a member of, and with what role. Multiple blogs supported.

Emanuela Castorina

This plugin in a multisite installation shows the ID of the current site/blog in the admin bar menu. The ID of the current site/blog is linked to the site info page. 
It adds also a custom column with site id information inside the sites list table. 
It can be installed only on a multisite.

Wp Show Site ID

This plugin in a multisite installation shows the ID of the current site/blog.

WPMU Default User Role vs Wp Show Site ID