Glipper, one of the most popular clipboard managers for GNOME finally got Ubuntu AppIndicator support in Natty. Previously, Glipper was a GNOME applet.
What makes Glipper interesting is that it uses plugins - some of the included plugins: support for Actions, Snippets and No-Paste services. Glipper can also display a popup (use Ctrl + Alt + C) for quick access.
The latest Glipper with AppIndicator support has been uploaded a few minutes ago into the Ubuntu 11.04 Natty Narwhal official repositories so you should get an update soon. For Ubuntu 10.10 Maverick Meerkat users, I've backported the latest Glipper from Natty so install it using the commands below:
sudo add-apt-repository ppa:nilarimogard/webupd8 sudo apt-get update sudo apt-get install glipper
Update: for a Glipper Monochrome icon (to go with the default Ubuntu theme - Ambiance), run these commands in a terminal:
wget http://ubuntuone.com/p/9F9 sudo mv 9F9 /usr/share/icons/hicolor/22x22/apps/glipper.png
(Monochrome icon thanks to David Callé!)
Once installed, press ALT + F2 and type "glipper" to run it.
Click here for more appindicators. There's also a list on AskUbuntu.