Full Text Search
MySQL's full text search capabilities are quite robust.  The full text search functionality is ideal for creating a search engine of your data.  By using natural language to query the database, MySQL will be able to find and rank results of those queries.  Many aspects of websites can be improve by adding search functionaly to the data.  The key to the web is making data as easy as possible to find.

Half of the search engine on this site is based off of the MySQL full text search capabilities.  The other half is based on Microsofts Indexing Service using the IXSSO COM object to query it from PHP.  There still needs to be some work to make the search result display better, but the actual search works quite well.

The MySQL full text search capablities are only available to tables that use the MyISAM database engine.  I usually use all InnoDB tables for my MySQL databases, but luckly, you can mix and match the table types inside of your MySQL database.

The key to running a full text search is the MATCH AGAINST keywords.