I use two different SQL Products:
1) SQL Server 2005/2008 now mostly 2008 because it supports geospatial data, as well as FileStream which allows you to store unstructured data (files) in the database. Can you say secure document management?

2) VistaDB which is a small footprint SQL Engine, whose Syntax is INTERCHANGEABLE with T/SQL 2005, and is .Net compatible. www.vistadb.com,

"The illiterate of the 21st century will not be those who cannot read and write, but those who cannot learn, unlearn, and relearn." ~ Alvin Toffler