The Deskbar is an all-in-one search bar. It is a Linux/Gnome panel applet that is similar to Google's (Windows only) Deskbar.
Its homepage is on the GNOME wiki at http://live.gnome.org/DeskbarApplet.
Downloads from SourceForge are at http://sourceforge.net/project/showfiles.php?group_id=122136&package_id=138163.
You can add your own search engines through the preferences dialog. Here, I've added my local library catalog.
This isn't a screenshot, but a still image from the screencast at http://browserbookapp.sourceforge.net/deskbar-screencast.html.
Raphaël Slinckx blogged about version 0.5. We're experimenting with the UI a bit, so that it's simpler. This means that a number of features evident from the 0.3 and 0.4 screenshots have been dropped - this software is still under construction. :)