Index and search with KDE's new Strigi
Strigi is quick at adding files into its index, but it's not perfect. It would be nice for the graphical search clients to offer more assistance in setting up common searches. For example, the strigiapplet allows you to type in a search string but offers no assistance in selecting which fields might be used to form your query. Having the search clients make an effort to parse human-readable time strings would make searching for files that were modified within a given period simpler.
All in all, Strigi is handy for finding files based on either their metadata, such as file size, ID3 tags, or file name, or their text content.