http://java.sun.com/products/jdbc/index.jsp
http://developers.sun.com/product/jdbc/drivers

Many database vendors deliver their own jdbc-drivers, like Oracle,
PostgreSQL, MySQL and so on. Check out the download pages for each
vendor. Some independent driver vendors, like iNet, deliver drivers for
several databases. Some drivers works on any platform, others are
platform-specific (depends on driver type). Most drivers support one
specific database. (It's possible that drivers using the TDS-protocol
can support different databases using this protocol, perhaps MSSQL and
Sybase simultaneously.)

The one driver that supports most different datasources is probably the
jdbc-odbc-bridge. It has some weaknesses, but in many cases it gets the
job done. If your app isn't overly complex, you don't want to manage a
large number of separate jdbc-drivers and odbc is a technology option,
it may do the trick. Just make sure that you won't suffer from it's
shortcomings.