LXSession / LXSession_Lite: Standard-compliant X11 session manager with shutdown/reboot/suspend supports via HAL and gdm (LXSession Lite is a stripped-down lightweight version without X11 session management support, and it's more stable)
LXAppearance: LXAppearance is a new feature-rich GTK+ theme switcher able to change GTK+ themes, icon themes, and fonts used by applications
Openbox: Lightweight, standard-compliant, and highly-configurable window manager (This is not developed by us, but we use it as our default window manager). This can be replaced by any other window manager like icewm, fluxbox, metacity, ...etc.
GPicView: A very simple, fast, and lightweight image viewer featuring immediate startup.