desktop environments available in pclinux repositories right now:
icewm(hmm!! win 95...)
there could be more but i don't remember and some doesn't have a task package to install them easily
i don't know if all of them are real desktops(could be just window decorations calling no taskbar, modifications maybe) but they exist and if you install them, you will find them in the login screen under the session button
please don't install all of them at once, it could be dangerous for your mental health!
i only had installed 4 at the same time but in reality i only use kde4 and gnome, gnome is my backup desktop but i only had used it 3 or 4 times the last year