I tend to use Gnome Do[1] as my launcher. I haven't observed any noticeable battery drain (on Arch) despite the fact that it runs in background.

There's a neat comparison of different launchers available on Wikipedia[2].

1: https://en.wikipedia.org/wiki/GNOME_Do 2: https://en.wikipedia.org/wiki/Comparison_of_desktop_applicat...

As someone mentioned previously the Alt + F2 (or F3) works well enough in XFCE most of time.

I'll give Cerebro a try...