A clipboard manager stores a certain number of entries of text that was last copied to the clipboard. Diodon is one such clipboard manager for Ubuntu. When it is running, the list of clipboard items it is maintaining can be accessed from the Panel.
For Ubuntu 12.04, you will first need to add the PPA repository:
$ sudo add-apt-repository ppa:diodon-team/stable
Install it using the package name
$ sudo apt-get install diodon
Once installed, it can be run from the Dash using the name Diodon.
Tried with: Ubuntu 14.04 LTS and Ubuntu 12.04.2 LTS