The Indicator Applet port to GTK3 has finally landed in Ubuntu 12.04 Precise Pangolin. This, along with some changes to the GNOME Panel default settings, finally "fix" the Classic (fallback) GNOME session in Ubuntu 12.04:
Touchpad Indicator was created with a very simple feature in mind: to allow you to easily enable / disable your laptop or netbook touchpad with a click but it slowly started gaining some other cool features.
Displex is an appindicator initially designed to provide similar functionality to the well-known "fusion-icon", but using an Ubuntu Indicator. However, Displex progressed and now provides a lot more features: it can be used to control the window decorations, screen rotation through Xrandr, switch between Metacity or Compiz compositing, provides AcerHK support and more.
For those who don't know, Wingpanel is a "super sexy space-saving top panel" created by the Elementary team that displays the Ubuntu indicators. Because it doesn't take the whole width of the screen and maximized windows go below it, it can save a lot of vertical screen space.
Lorenzo @ atareao.es has created yet another Ubuntu indicator: Google Reader Indicator, which you can use to take a quick look at your unread Google Reader items.