If you are a database person, you will be pleased to see that Linux is very well covered in this area.
postgreSQL is a high-powered database available on Mandrake and RH CD (free, unrestrictive BSD license).
mySQL http://www.MySQL.com/ GPL database, simpler and easier than postrgreSQL, yet very very capable. Favourite among many database developers. Like postgreSQL, mySQL is not meant to be just a personal database, and it may be hard to use it as such.
There are also commercial databases which are free for personal use, e.g. Sybase for Linux ( http://www.sybase.com:80/sqlserver/linux/aselinux_install.html ) and Interbase ( http://www.interbase.com/downloads/products.html). There is also Oracle for Linux: http://platforms.oracle.com/linux/index_lin.htm. For an Oracle-Linux howto, see: http://jordan.fortwayne.com/oracle/index.html[an error occurred while processing this directive]