WPMU Dev is THE source for Wordpress MultiSite plugins and support. I've recently switched from 8 single site wordpress installations to 1 multisite network that houses all of my sites. This has been a very challenging move, but with the help of WPMU Dev, I have access to a wide array of plugins that are designed JUST FOR MULTISITE. And the best part is, most of their plugins integrate with each other. This alllows the greatest flexibility when planning the features of your site. And to top it all off, I've received excellent support on some very technical plugin customizations. Their developers really know what they are doing and they've often gone above and beyond to make sure that I can create the functionality that I need. This is a great company that is getting better every day. I can't wait to see what they come up with next...