Those Gnome fellas have everything
Here's another desktop search tool with a fetish for your system tray, but only if you run Gnome. KDE users can feel free to hunt for it in the beloved K menu.
Tracker, like most others in this test, is still to reach the pivotal 1.0 release and yet it too is robust, elegant and effective. Available from the software repositories of most distros, Tracker is a bit more fussy about getting started. How else would you define a file indexer where indexing is disabled by default?
Use the tracker-preferences command to launch the Preferences window and enable indexing. Unlike the other tools, you can configure Tracker to index certain directories, but not actively watch them. That is, if you change the files within a directory that Tracker isn't watching, the changes won't reflect in the index.
The Preferences window comprises several tabs, each of which deals with different aspects of Tracker. You can specify the paths and patterns that you want Tracker to ignore from the Ignored Files tab and enable Evolution email indexing from the Email tab.
Future versions will support indexing browser bookmarks, history, notes, tasks etc. You can't change the default Tracker behaviour of displaying 10 results per page, so keep an eye out for the Next and Previous buttons to scroll through pages.
When you click on a result, Tracker shows you details about the file, such as its dimensions if it's an image. Tracker also lets you add tags to each of the indexed files. You can use the same tags for different files and thus create a collection of grouped content that can be accessed easily.
Unfortunately, this isn't very reliable because Tracker sometimes fails to display all files assigned the same tag.
Price: Free under GPL
A definite podium contender if it can improve its launch time and fix the broken tagging feature.