Catfish
Catfish is a versatile file searching tool.

Features
Catfish is a frontend for different search engines (daemons). The interface is intentionally lightweight and simple, using only GTK+ 2. You can configure it to your needs by using several command line options.
Supported backends:
find, (s)locate, doodle, tracker, beagle, strigi and pinot
Requirements: PyGtk2, Glade2, python-xdg¹, dbus²
¹ python-xdg is optional but strongly recommended
² dbus is required for strigi and pinot
Current State

Development of Catfish is currently stalled. There are plans for a new version with a revamped interface. Some code has been written but there is no time schedule to make a release anytime soon.
Download
Download: catfish v0.3.2 (35kB) (ChangeLog)