Remote Connection Manager is a GTK application that provides an easy way to initiate connections to remote machines. It's primary goal is to provide a GUI to launch ssh, telnet and rdesktop type of applications, however it is highly configurable.
SeamlessRDP is an implementation of seamless windows server components for rdesktop based on code contributed by Cendio AB http://www.cendio.com/seamlessrdp/ . In seamless mode, rdesktop creates a X11 window for each window on the server side.