GNOME Clipboard Daemon

GNOME Clipboard Daemon is a program that keeps the content of your X clipboard in memory, so the clipboard won' get lost even after you close the application you copied from. It's a daemon - it has no GUI. You start it and it'll run in the background and Just Work(tm).
from: http://members.chello.nl/~h.lai/gnome-clipboard-daemon/index.html

installation for ubuntu:
wget -c http://frankandjacq.com/ubuntuguide/gnome-clipboard-daemon-1.0.bin.tar.bz2
sudo tar jxvf gnome-clipboard-daemon-1.0.bin.tar.bz2 -C /usr/bin/
sudo chown root:root /usr/bin/gnome-clipboard-daemon
sudo chmod 755 /usr/bin/gnome-clipboard-daemon
sudo gnome-clipboard-daemon &