Glom is a GUI that allows you to design MySQL table definitions and the relationships between them. It also allows you to edit and search the data in those tables.
KSqlAnalyzer is a tool for easy accessing the data of a MS-SQL-Database. The functionality and the look&feel are similar to the program 'SQL-Query-Analyzer' written by Microsoft.
mysqldiff is a Perl script which compares the data structures (i.e. table definitions) of two MySQL databases and returns the differences as a sequence of MySQL commands suitable for piping into mysql which will transform the structure of the first database to be identical to that of the second.