bmpanel2 is a nice NETWM-compatible panel for X11, featuring look and
feel customization via themes, a bunch of widgets (desktop switcher, 
taskbar, launchbar, systray, clock, etcetera), pseudo-transparency support,
small executable size (~80kB), and small memory footprint (about 2-4 MB).

Configuration of bmpanel2 is done via bmpanel2cfg program or by editing
the ~/.config/bmpanel2/bmpanel2rc file.  Themes can be installed locally
by placing them in the ~/.local/share/bmpanel2/themes directory.