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.
Install through Terminal:
sudo add-apt-repository ppa:nilarimogard/webupd8 sudo apt-get update sudo apt-get install glipper
To get Glipper's Monochrome icon that goes with the default Ubuntu theme "Ambiance":
wget http://ubuntuone.com/p/9F9 sudo mv 9F9 /usr/share/icons/hicolor/22x22/apps/glipper.png
Enjoy
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I also recommend "ClipIt" as well.