*custom size history;
*editable history of the clipboard with a search function;
*keyboard shortcuts for basic operations;
*command: you can set the actions or commands that are executed if copied to the clipboard the text meets certain criteria. This can be used, for example, to start the video player, if the copied text contains the URL of the multimedia content;
*support of images: when you copy a selection in GIMP or image in Shutter, its a preview will be shown in the system tray, as well as the rest of the clipboard history. It definitely will not work if you copy the image file (such as Nautilus), since in this case it is treated as a file;
*command line support: all operations can be performed from the command line.