You could try Diodon, a simple and lightweight clipboard manager for Gnome with application indicator support. Apparently it aims to be the best integrated clipboard manager for the Gnome/GTK+ desktop, and it's the one I know that's still actively developed.
News/Questions about the application can be found on the official homepage.
I use it on Ubuntu 14.04 and it's important to say that in order for Diodon to work, Zeitgest must be enabled (see the question "Diodon does not save anything copied to the clipboard" on Ask Ubuntu)
This is a screenshot of the Diodon preferences:
This is the Diodon application indicator containing three elements that were just added to the clipboard: