Josh Maxwell

The <a href="http://ardentpixels.com/" rel="nofollow ugc">Ardent Pixels’</a> Gravatar plugin adds the gravatar photo associated with the user’s email to their profile page. If they do not have a gravatar account, it displays a link to create one. And is MultiSite compatable!
This plugin does not add gravatar support to your theme.
<h3>Notes</h3>
= Donations = 
Feel free to <a href="http://ardentpixels.com/josh/contact/" rel="nofollow ugc">donate</a> if you liked this plugin.

AP Gravatars

A simple plugin that adds the gravatar photo associated with the user's email to their profile page... MultiSite compatable!

Joshua Parker

Plugin allows a super admin to put his/her entire network, main site, or subsites into maintenance mode.

WPMS Site Maintenance Mode

Provides an interface to make a WPMS network unavailable to everyone during maintenance, except the admin.

AP Gravatars vs WPMS Site Maintenance Mode