I can recommend Parcellite as it is not only a very sound and at the same time lightweight Clipboard Manager, but you can also save your "favorites" in its Actions tab.
Go to Preferences > Actions, and then enter a label for your favorite item under the Action column, and then go to Command column to simply enter your favorite text preceded by the command
parcellite (For example; Action: my email address Command: parcellite firstname.lastname@example.org)
To use your favorite text, you'll only need to press
Ctrl+Alt+A and then choose its label (e.g. "my email address") from the popup menu, followed by the usual
Ctrl+V, and there you have your email address instantly pasted.