I think a really nice plugin would be to have a plugin that displays admin status so people with servers that require users to get buildrights would know if an admin was available. If the admin is online, it would tell you that, and if they're offline, it shows their last visit date. The colored text could be optional, but I think it would visually make it easier to understand. The signs would automatically update when they sign in/out (or it could be on a timer for less memory usage?). Below is my crappy rendition of what it would look like. With an AFK system http://imageshack.us/photo/my-images/818/adminscopy2.jpg/
I like this... i'm still kinda learning how to make plugins but i'll give it a shot if you'd like. ^^